Geology

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Acidic rock

Acidic rock refers to an igneous rock that consists mostly of light coloured

minerals and has more than 66% free or combined silica.


Actinolite

Actinolite has the formulae Ca2(Mg,Fe)5Si8O22(OH)2 and a relative hardness of 6.

It commonly occurs in crystalline schists, often being the chief constituent of

green-coloured schists and greenstones. It is used somewhat as an asbestos

material.


Adamantine

Adamantine refers to a brilliant luster like that of a diamond. Results from a

mineral having a high index of refraction.


Adamite

Adamite has the formulae Zn2(AsO4)(OH) and a relative hardness of 4.

It has brilliant fluorescence, is of scientific interest and is much desired by

collectors.


Adularia

Adularia (Moonstone) is a semi-precious, clear, transparent, glassy form of

potash felspar which is found mainly in the crevices of crystalline schists and

gneisses, often in beutifully perfect crystals. It has sometimes a pearly,

opalescent reflection or play of colours.


Aegirite

Aegirite has the formulae NaFe(Si2O6) and a relative hardness of 7.

It is a rock-forming mineral found mainly in rocks rich in soda and poor in

silica. Named after Aegir, Icelandic god of the sea.


Agalmatolite

Agalmatolite is a soft species of mineral, also called pagodite and

figure-stone, used by the Chinese for carving, especially into grotesque

figures.


Agaric Mineral

Agaric Mineral is one of the purest native carbonates of lime. It is chiefly

found in the clefts of rocks and at the bottom of some lakes.


Agate

Agate is a semi-precious stone comprised mainly of silica. It is a compact

variety of chalcedony. It has a pattern of banding which occurs due to chemical

admixtures of haematite, limonite and other minerals.


Alabaster

Alabaster is naturally occurring hydrated calcium sulphate.


Albite

Albite has the formulae NaAlSi3O8 and a relative hardness of 7.

It is widely distributed, rock-forming mineral. Present in pegmatite dikes and

may be found in crystals.


Alkaline rock

Alkaline rock refers to any rock which contains more than average amounts of

potassium bearing and sodium bearing minerals.


Allanite

Allanite has the formulae (Ce,Ca,Y)2(Al,Fe)3(SiO4)3(OH) and a relative hardness

of 6.

It occurs as a minor constituent of many igneous rocks and is frequently

associated with epidote. Found in some magnetic bodies.


Allemontite

Allemontite is a natural alloy of arsenic and antimony. It has a relative

hardness of 4.


Almandine

Almandine is a variety of precious garnet, reddish or violet in colour.


Alteration

Alteration refers to physical or chemical change in a rock or mineral after its

original formation. Can result in new minerals or in textural changes in the

rock.


Alumina

Alumina is aluminium oxide and occurs as ruby, sapphire, bauxite.


Alunite

Alunite has the formulae KAl3(SO4)2(OH)6 and a relative hardness of 4.

It is usually formed by sulphuric acid solutions acting on rocks rich in

alkalic feldspar. Used in the production of alum.


Alunogen

Alunogen is a fibrous aluminium sulphate found in volcanic debris, clays,

feldspathic rocks which contain pyrites, and often as an inflorescence on the

walls of mines and caves.


Amblygonite

Amblygonite has the formulae (Li,Na)Al(PO4)(F,OH).

It has a relative hardness of 6.

It occurs in lithium and phosphate rich granite pegmatites. Associated with

spodumene, apatite, tourmaline, lepidolite.


Amethyst

Amethyst is a precious stone. It is quartz coloured with manganese.


Amorphous

Amorphous refers to 'Without form'. The term is applied to rocks and minerals

that lack definite crystal structure.


Amphibole

The amphiboles are a large group of minerals, the silicates of many different

bases, the commonest being alumina, iron oxide, lime, magnesia and the alkalis.

They are constituents of many crystalline igneous rocks and of metamorphic

schists. In many of their properties they closely resemble the pyroxenes. They

occur generally in black or dark green crystals, usually long, narrow and

blade-like, and owing to their perfect cleavages their surfaces are smooth and

bright. The commoner varieties are hornblende, actinolite and tremolite.


Amygdaloidal

Amygdaloidal is a name given to igneous rocks, usually old lava flows, full of

almond-shaped cavities which have been filled up with secondary minerals, such

as calcite, agate or the zeolites. These cavaties vary in size up to several

centimeters across and were formed while the rock was still fluid and in motion.


Amygdule

Amygdule refers to a mineral containing cavity in an igneous rock formed by

escaping gas.


Anaclime

Anaclime has the formulae NaAlSi2O6ù2H2O and a relative hardness of 6.

It is found in the cavities of intrusive and volcanic igneous rocks; often as

clear shiny crystals and is associated with calcite and zeolites.


Anatase

Anatase has the formulae TiO2 and a relative hardness of 6.

It is a form of rutile found in granite, gneiss, mica schist, maetamorphic

limestone, and dolomite. May be present as an accessory mineral in the rocks or

in a quartz vein traversing it. It is used as a coating for welding rods and as

a derivative of titanium.


Andalusite

Andalusite is a mineral formed by the metamorphism of aluminous shales and

slate. It is used in the manufacture of spark plugs and other porcelains and

may serve as a gem stone if it is clear and transparent. It is named from

Andalusia, a province of Spain. It has the formulae Al2SiO5 and a relative

hardness of 8.


Andesine

Andesine has the formulae NaAlSi3O8.

It has a relative hardness of 6.


Andesite

Andesite is a crystalline igneous rock, occuring mostly in lava flows, but

sometimes in dykes and veins. It consists proncipally of plagioclase felspar,

and is often porphyritic, showing large crystals of felspar scattered through a

fine-grained mass, usually of small felspar crystals, but often containing much

glassy material. Andesite forms most of the recent volcanic rock of the Andes,

and is thus named after the Andes.


Anglesite

Anglesite is a common, minor ore of lead formed by the oxidation of galena.It

has the formulae PbSO4 and a relative hardness of 3. It is found in the upper,

oxidzed portions of lead veins and is named after the Island of Anglesey.


Anhydrite

Anhydrite is a mineral consisting of sulphate of lime. It has rectangular

cleavage fragments and occurs in a manner similar to gypsum and often found

with it but not as common. It is found in the cap rock of salt domes and in

limestone rocks. The name comes from the Greek meaning 'without water'. It has

the formulae CaSO4 and a relative hardness of 4.


Annivite

Annivite is a variety of terahedrite containing bismuth and usually iron and

zinc.


Anorthite

Anorthite is a widely distributed and abundant rock-forming feldspar. It has

the formulae (Na,Ca)AlSi3O8 and a relative hardness of 7.


Anthophyllite

Anthophyllite is a mineral occuring in crystalline schists rich in magnesium.

It has the formulae (Mg,Fe)7Si8O22(OH)2 and a relative hardness of 6.


Anthracite

Anthracite (stone coal) is a kind of coal distinguished by its great hardness,

its high proportion of carbon, and the great heat given out in burning.


Antimonite

Antimonite is an antimony ore. It was used by the Greeks as a cosmetic for

darkening the eyelids.


Antimony

Antimony has the formulae Sb.

It has a relative hardness of 4.

It is a native semimetal and difficult to distinguish from arsenic. Rather

brittle and a poorer conductor of heat and electriciy than native metals.


Apatite

Apatite has the formulae Ca5(F,Cl,OH)(PO4)3.

It has a relative hardness of 5.

It is widely distributed as an accesory constituent in all classes of rock.

Found in crystals and masses. Crystallized apatite has been extensivley for

fertilizer. Transparent varieties of fine colour are sometimes used for gems -

but it's too soft for extensive use.


Aphanitic rock

Aphanitic rock refers to a rock in which the crystalline constituents are too

small to be distinguished without magnification.


Apophyllite

Apophyllite has the formulae KCa4Si8O2O(OH)ù8H2O.

It has a relative hardness of 5.

It is a hydrothermal mineral filling cavities in basalt and tufaceous rocks.

Associated with stilbite, scolecite, calcite, prehnite, analcime.


Aragonite

Aragonite has the formulae CaCO3.

It has a relative hardness of 4.

It forms easily in a sedimentary environment but only stable in metamorphic

rocks formed at high temperatures.


Arfvedsonite

Arfvedsonite has the formulae Na2-3(Fe,Mg,Al)5Si8O22(OH,F)2.

It has a relative hardness of 6.

It is typical of alkaline plutonic rocks that are rich in iron.


Argentite

Argentite is an important primary silver ore. The name is from Latin meaning

'silver'. Occurs disseminated in galena and in the cementation zone of lead and

zinc deposits. Associated with cerussite, chlorargyrite, native silver. It has

the formulae Ag2S and a relative hardness of 3.


Argillaceous

Argillaceous refers to composed mostly of or containg clay; such as shale.


Arsenates

Arsenates refers to minerals in which arsenate (AsO4) is an important part.


Arsenic

Arsenic is a a trivalent and pentavalent, solid, poisonous element that is

commonly metallic steel-gray, crystalline and brittle. It is used in medicine

and in the manufacture of electronic components. It has a garlicky odor but

otherwise it is difficult to distinguish from antimony. It is a relatively rare

mineral found in veins in crystalline rocks associated with silver, cobalt, or

nickel ores. It has the symbol As.


Arsenopyrite

Arsenopyrite is the most common mineral containing arsenic. It occurs with tin

and tungsten ores in high temperature deposits as a deposition from hot waters.

Frequently associated with gold. Also found with copper and silver ores. It has

the formulae FeAsS and a relative hardness of 6.


Asbestos

Asbestos is a fibrous mineral with a high melting and combustion point. Cloth

was made of it by the ancient Egyptians.


Atacamite

Atacamite is the native hydrous oxychloride of copper. It is a comparatively

rare mineral occuring in arid regions in the upper oxidized zone of copper

deposits. It has the formulae Cu2Cl(OH)3 and a relative hardness of 4.


Augite

Augite has the formulae (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6.

It has a relative hardness of 6.

It is an important rock forming mineral. Chiefly found in dark coloured igneous

rocks, especially those whose magmas were rich in iron, calcium and magnesium.

Seldom found in rocks that contain much quartz. A common memeber of the

pyroxene group. Told from the amphibole group by cleavage.


Autunite

Autunite has the formulae Ca(UO2)2(PO4)2ù10-12H2O.

It has a relative hardness of 3.

It has strong fluorescence. A secondary mineral found in the zone of oxidation

and weathering of uranite or other uranium minerals. Used as an ore of uranium.


Axinite

Axinite has the formulae Ca2(Fe,Mn)Al2(BO3)(Si4O12)(OH).

It has a relative hardness of 7.

It occurs in cavities in granite and in the contact zones surrounding granite

intrusions.


Azurite

Azurite has the formulae Cu3(CO3)2(OH)2.

It has a relative hardness of 4.

It is a minor ore of copper with an intense azure-blue colour. Alters to

malachite. Associated with limonite, calcite, chalcocite, chrysocolla and other

secondary copper minerals. Reacts vigorously with hydrochloric acid.


Barite

Barite has the formulae BaSO4.

It has a relative hardness of 3.

It is major ore of barium. Has a high SG for a light coloured mineral. Common

gangue mineral in hydrothermal veins or as a repacement mineral in veins of

limestone and dolomite. Associated with lead, silver and antimony sulphides.


Barytes

Barytes was the first mineral to be found to be luminescent when heated, and

led to the discovery of the luminescence of minerals. It has a relative

hardness of 3.5.


Basanite

Basanite is a smooth, black siliceous mineral.


Basic rock

Basic rock refers to an igneous rock with a low percentage of silica and a high

percentage of pyroxene, hornblende, and labradorite.


Bauxite

Bauxite is a sedimentary rock group of various aluminium oxides, a principal

ore of aluminium, found in France and Jamaica. Bauxite was named after the

place where it was first found, Les Baux in France. It has a relative hardness

of 1 to 3.


Bedding

Bedding refers to the arrangement of sedimentary rocks in about parallel layers

or strata which correspond to the original sediments.


Beryl

Beryl (beryllium aluminium meta-silicate) has the formulae Be3Al2Si16O18 and a

relative hardness of 8.

It has a characteristic six-sided outline and is used as a gem stone of various

colours, its green variety being emerald. Beryl is also the major source of the

rare element beryllium, a light metal similar to aluminum. Beryl is quite

common and occurs usually in granite rocks, mica schists and with tin ores.


Beryllium aluminium meta-silicate

see "Beryl"


Biotite

Biotite has the formulae K(Mg,Fe)2(Al,Fe)Si3O10(OH,F)2 and a relative hardness

of 3.

It is a widely distributed rock forming mineral and occurs in igneous and

metamorphic rocks and is a common member of the mica group.


Bismuthinite

Bismuthinite has the formulae Bi2S3 and a relative hardness of 2. It is a rare

ore of bismuth. Occurs in veins that show definite relations to igneous rocks.


Bituminous rocks

Bituminous rocks refers to rocks that contain tar, petroleum, or asphalt.


Blende

Blende is a zinc ore. It generally contains more than half its weight in zinc,

a quarter sulphur and often a small amount of iron.


Bloodstone

Bloodstone is a dark green variety of chalcedony.


Bohemian garnet

see "Pyrope"


Bole

Bole is an earthy mineral occuring in amorphous masses , and composed chiefly

of silica with alumina, iron and occasionally magnesia.


Boracite

Boracite has the formulae Mg3B7O13Cl and a relative hardness of 7. It occurs

associated with beds of halite, anhydrite, and gypsum. It is formed by the

evaporation of bodies of salt water.


Borates

Borates refers to a group of minerals in which the borate radical (BO3) is an

important constituent.


Borax

Borax (sodium tetraborate) is the sodium salt of pyroboric acid. It has the

formulae Na2B4O710H2O and a relative hardness of 3. It forms large transparent

six-sided prisms which have an alkaline reaction, effloresce in air, and when

heated swell-up and melt to a transparent glass. Borax is used in the

manufacture of enamel-ware, glass, as an antiseptic and is a food preservative.

It is also useful in brazing and silver soldering as it dissolves metalic

oxides, thus cleaning the surfaces of the metals to be united.


Bornite

Bornite has the formulae Cu5FeS4 and a relative hardness of 3. It is an ore of

copper with a colourful tarnish, widely occurring, it is found in basic rocks

and metamorphic deposits.


Botryoidal

Botryoidal refers to resembling a bunch of grapes. A mineral of this type

appears to have a surface covered with spherical bulges.


Boulangerite

Boulangerite is a lead ore. It contains 55 percent lead. It has a relative

hardness of 2.5.


Bournonite

Bournonite is an ore of lead, copper, and antimony which often exhibits twinned

crystals. It occurs in veins formed at moderate temperatures and has the

formulae PbCuSbS3 and a relative hardness of 3.


Breccia

Breccia is a rock consisting of angular fragments of any kind, united by a

matrix. The shape of the components indicates that they have been produced by

fracture, and have not been subjected to rounding by attrition. Fault breccia

is often found between the two walls of a geological fault, and is due to the

breaking down of the rocky walls when grinding on one another. Mineral veins

are often formed in fissures, and are brecciated later by movement of the

walls. Another kind of breccia is produced when hot molten lava enters a lake

or a stream; it is suddenly cooled and solidified, being at the same time

shattered by the clouds of steam that are formed. Braccias differ from

conglomerates in the angular nature of their fragments, and in the method of

their origin.


Brimstone

Brimstone is another name for sulphur.


Bronzite

Bronzite is a pyroxene which is co called from its sub-metallic lustre

resembling tarnished bronze.


Brookite

Brookite is a source of titanium but deposits are usually too small to be of

commercial use. It has the formulae TiO2 and a relative hardness of 6.


Brown Spar

Brown Spar is the name given to some crystalline varieties of dolomite tinged

with peroxide of Iron


Brucite

Brucite is a decomposition product of magnesium silicates, especially

serpentine. It has the formulae Mg(OH)2 and a relative hardness of 3.

It is found in Texas, where it is white with a grey, green or blue tinge and is

used in sugar-refining.


Cacholong

Cacholong or mother-of-pear opal and sometimes Kalmuck agate, is a variety of

opal, usually grey in colour, milk white or bluish white, and resembling

mother-of-pearl. It is banded with layers of different colours and is a most

attractive ornamental stone.


Calamine

Calamine is a zinc ore.


Calcareous

Calcareous refers to containing calcium carbonate or calcite.


Calcic

Calcic refers to containing calcium.


Calcite

Calcite has the formulae CaCO3.

It has a relative hardness of 3.

It effervesces vigorously with HCl. Clear specimens exhibit double refraction.

Occurs as widespread sedimentary rock masses such as limestone. Crystalline

metamorphosed limestones are called marbles. Fine grained deposits form chalk.

Variety: onyx.


Calcium Silicate

see "Sphene"


Caliche

Caliche is naturally occurring sodium nitrate found in Chile.


Cannel Coal

Cannel Coal is a dull black coal which breaks with a conchoidal fracture and

does not soil the fingers when handled. In some respects it resembles jet. It

is easily cut, and will take a high polish. It contains a large proportion of

volatile constituents making it suitable for gas manufacture, and it burns with

a bright white flame.


Carbonaceous

Carbonaceous refers to composed chiefly of organic carbon. (i.e. carbon derived

from plant and animal remains.)


Carbonates

Carbonates refers to minerals, such as calcite, where the carbonate radical

(CO3) is an important constituent.


Carnallite

Carnallite is a source of potassium coumpounds and magnesium. Has a bitter

salty taste and has the formulae KMgCl3ù6H2O and a relative hardness of 3.


Carnelian

Carnelian is a clear red chalcedony, a semi-precious gemstone, consisting of

quartz with iron impurities which give it a translucent red colour. Carnelian

is found mainly in Brazil, Japan and India.


Carnotite

Carnotite has the formulae K2(UO2)2(VO4)2ù3H2O.

It has a relative hardness of 1.

It is an ore of uranium and vandium. Found in sand, sandstones and around

petrified trees. Probably formed as a deposition from meteoric waters. Strongly

radioactive.


Cassiterite

Cassiterite is the principal ore of tin. It is widely distributed in small

amounts but commerically available in only a few localities. It is frequently

associated with wolframite. It is also found as rolled pebbles in placer

deposits ('stream tin') but is usually found in veins associated with quartz,

in or near granitic rocks. It has the formulae SnO2 and a relative hardness of

7.


Celestine

Celestine is a natural sulphate of strontium.


Celestite

Celestite has the formulae SrSO4.

It has a relative hardness of 4.

It often found disseminated through limestone or sandstone, or lining cavities

in such rocks. Associated with calcite, dolomite, gypsum, sulphur, fluorite.

Also found as a gangue mineral in lead veins. Used to prepare nitrate of

strontium for fireworks and tracer bullets and in the refining of beet sugar.


Cerussite

Cerussite has the formulae PbCO3.

It has a relative hardness of 4.

It is an important and widely distributed supergene lead ore formed by the

action of carbonated waters on galena in the upper zone of lead veins. Often

found associated with galena and sphalerite.


Chabazite

Chabazite is a mineral of secondary origin found lining cavities in volcanic

and intrusive igneous rocks. It has the formulae Ca(Al2Si4)O126H2O and a

relative hardness of 5.


Chalcanthite

Chalcanthite is a minor ore of copper found only in arid regions. It occurs

near the surface in copper veins and is often deposited on iron from the water

in copper mines. It is used in calico printing, insecticides and for industrial

purposes. It has the formulae CuSO45H2O and a relative hardness of 3.


Chalcedony

Chalcedony is a variant of quartz comprised of silica. Chalcedony was named

after Chalkedon, near Istanbul. It was traditionally used for decorative

objects and amultes. It has a relative hardness of 7.


Chalcocite

Chalcocite is one of the most important copper ore minerals. It occurs

primarily in enriched zones of sulphide deposits. It has the formulae Cu2S and

a relative hardness of 3.


Chalcopyrite

Chalcopyrite has the formulae CuFeS2.

It has a relative hardness of 4.

It is the most widely occuring copper mineral and one of the most important ore

sources of that metal. Occurs as an original constituent of igneous rocks, in

pegmatic dikes, and in contact with metamorphic deposits. May carry gold or

silver and become an ore of those metals.


Chalcosine

Chalcosine is an important copper ore. It was discovered in the 16th century.


Chert

Chert is a mineral very similar to flint, but coarser and less uniform in

colour. It is found principally in association with limestones, especially in

the carboniferous limestone of Ireland where beds of it are found several

hundred feet thick. It appears to have resulted from the solution and

redeposition of the silica of certain kinds of fossils, particularly of

sponges, with the pointed spicules of which it is often filled. Radiolarian

chert is a streaky, dark-grey, brown or reddish rock which under the microscope

is seen to consist of innumerable shells of Radiolaria firmly united together

by a siliceous cementing material.


Chili Saltpetre

see "Cubic Nitr"


Chlorite

Chlorite has the formulae (Mg,Fe)6(AlSi3)O10(OH)8.

It has a relative hardness of 3.

It is a mineral group whose members usually exhibit a charactersitic green

colour. The formula above is for 'green mica'. Distinguished from muscovite and

green phlogopite by a lack of elasticity.


Chondrodite

Chondrodite has the formulae (Mg,Fe)3(SiO4)(OH,F)2.

It has a relative hardness of 7.

It is a common metamorphic mineral in dolomitic marbles.


Chromite

Chromite has the formulae FeCr2O4.

It has a relative hardness of 6.

It is slightly magnetic. The only ore of chromium. A common constituent of

peridotite rocks and the serpentines derived from them. Also associated with

corundum. One of the first minerals to separate from a cooling magma. Chromium

is widely used in metal plating and in stainless steel.


Chrysoberyl

Chrysoberyl has the formulae BeAl2O4.

It has a relative hardness of 9.

It occurs in granite rocks, pegmatites, and in mica schists. Frequently in

river sand and gravels. Serves as a gem stone: alexandrite and "cats eye" which

can be of great value.


Chrysocolla

Chrysocolla has the formulae (Cu,Al)2H2Si2O5(OH)4ùnH2O.

It has a relative hardness of 4.

It is a minor ore of copper. A mineral of secondary origin, occuring in the

oxidized zones of copper veins. Associated with malachite, azurite, cuprite,

native copper. Named from two Greek words meaning 'gold' and 'glue'.


Chrysostom

Chrysostom is a gem stone of beryllium aluminate.


Cinnabar

Cinnabar (vermilion) is a red crystalline form of mercuric sulphide. It has the

formulae HgS and a relative hardness of 3.

It often has a bright red colour. The only important source of mercury and it's

found in few localities. Occurs as vein fillings near recent volcanic rocks and

hot springs. Used in scientific equipment, in drugs, and with tin in silvering

mirrors. Many other uses.


Clastic rock

Clastic rock refers to a sedimentary rock comprised of fragments of preexisting

rocks that have been transported and deposited.


Clay

Clay refers to a soft sediment or deposit that is plastic when wet and

comprised of very fine-grained materials, mainly hydrous aluminum silicates.


Cleavage

Cleavage refers to a mineral is said to possess cleavage if when it breaks it

yields definite plane surfaces. Cleavage can be perfect as in micas or, in some

minerals, completely lacking. Cleavage is always parallel to crystal faces.


Cleveite

Cleveite is a uranium-containing mineral, of interest owing to the fact that

when heated with dilute sulphuric acid it liberates considerable quantities of

occluded helium. It was this property which first led to the discovery of the

element helium.


Clinozoisite

Clinozoisite has the formulae Ca2Al3Si3O12(OH).

It has a relative hardness of 7.


Cobalt glance

see "cobaltite"


Cobaltite

Cobaltite (cobalt glance) is an ore of cobalt consisting of a cobalt

arsenosulphide of the formulae CoAsS and has a relative hardness of 6.

It is usually found in high temperature deposits, disseminated in metamorphic

rocks, or in vein deposits with other cobalt and nickel minerals.


Coelestine

Coelestine is a mineral used in pyrotechnics and a s a source of strontium.

Occassionaly it is cut and used as a gem stone. It has a relative hardness of

3.5.


Colemanite

Colemanite is a major source of borax and has a relative hardness of 5. It

occurs in high temperature hydrothermal veins or disseminated in metamorphic

rocks associated with other cobalt and nickel sulphides/arsenides.


Columbite

Columbite has the formulae (Fe,Mn)(Nb,Ta)2O6 and a relative hardness of 6.

It shows a bluish iridescent fracture surface. The main ore of niobium and

tantalum; used in metallurgy to create heat-resistant alloys and in the rust

proofing of stainless steel.


Concretion

Concretion refers to an accumulation of mineral matter when mineral particles

become cemented together into an orderly, rounded form.


Contact metamorphism

Contact metamorphism refers to metamorphism resulting from the intrusion of

magma which takes place at or near the contact point with the molten rock.


Copper

Copper is one of the essential metals of modern civilization. Native copper is

found in copper veins but copper sulphides are the principal source ores of the

metal. It has the formulae Cu and a relative hardness of 3.


Cordierite

Cordierite is found as an accessory mineral in granite, gneiss, schists, and in

contact metamorphic zones. Transparent specimens of good colour have been used

as a gem stone. It has the formulae Mg2Al4Si5O18 and a relative hardness of 8.


Corundum

Corundum is common as an accessory mineral in metamorphic rocks and as an

original constituent of certain igneous rocks. Color differences give rise to

several varieties of gem, notably, ruby and saphire. The deep red ruby is one

of the most valuable gems, second only to emerald and diamond.It has the

formulae Al2O3 and a relative hardness of 9.


Covellite

Covellite is an indigo-blue material found in most copper deposits, usually as

a coating in the zone of sulphide enrichment. It has the formulae CuS and a

relative hardness of 2.


Cristobalite

Cristobalite is present in many siliceous volcanic rocks as a lining in

cavities. Upon heating to 1470 C it becomes nearly transparent. On cooling it

assumes its initial white translucent appearance. It has the formulae SiO2 and

a relative hardness of 7.


Crocoite

Crocoite is a rare mineral found in the oxidized zones of lead deposits where

lead veins have traversed rocks containing chromite. Not abundant enough to be

of commercial value although it does contain chromium. It's name is Greek and

means 'saffron', an allusion to its colour. It has the formulae PbCrO4 and a

relative hardness of 3.


Cross-stone

see "Harmotome"


Cryolite

Cryolite has the formulae Na3AlF.

It has a relative hardness of 3.

It often found enclosing brown siderite and grey galena. Always occurs in

pegmatites where it's probably a precipitate from flouride rich solutions. Used

in the manufacture of sodium salts, certain kinds of glass and porcelain, and

as a flux for cleaning metal surfaces.


Crystal

Crystal refers to a solid mineral having a regular geometric shape and bounded

by smooth flat surfaces(called crystal faces).


Crystal symmetry

Crystal symmetry refers to the repetitive pattern of crystal faces caused by

the orderly internal arrangements of atoms within a mineral.


Cubic Nitre

Cubic Nitre (sodium nitrate, Chili Saltpetre) is a mineral found mainly in the

Tarapaca district of Chile.


Cuprite

Cuprite has the formulae Cu2O.

It has a relative hardness of 4.

It is an important ore of copper. Found in the upper oxidized portions of

copper veins. Commonly found in crystal forms.


Danburite

Danburite has the formulae CaB2Si2O8.

It has a relative hardness of 7.


Datolite

Datolite has the formulae CaBSiO4(OH).

It has a relative hardness of 6.

It is a mineral of secondary origin found usually in cavities in basalt lavas

and similar rocks.


Delvauxite

Delvauxite is a mineral source of phosphate. It has a relative hardness of 2.5.


Destinezite

Destinezite is a mineral. It is a source of phosphate. It has a relative

hardness of 3.


Detrital sediment

Detrital sediment refers to deposited rock and mineral fragments.


Diamond

Diamond has the formulae C.

It has a relative hardness of 10.

It is the hardest naturally occuring mineral and the most important of the gem

stones. Occurs in pale shades of several colours, deep shades are rare. Gem

quality diamond is transparent, of attractive colour, and without internal

fractures or inclusions of other materials.


Diaspore

Diaspore has the formulae AlO(OH).

It has a relative hardness of 7.

It is a constituent of bauxites and a major source of aluminum.


Dike

Dike refers to a wall-like body of igneous rock that cuts across layers of

surrounding rocks.


Diopside

Diopside has the formulae CaMgSi2O6 and a relative hardness of 6.

It is usually found as a contact metamorphic mineral in crystalline limestones.

Transparent varieties have been cut and used as gemstones.


Dioptase

Dioptase has the formulae CuSiO2(OH)2 and a relative hardness of 5.

It is found in the oxidation zone of copper deposits, in cavities of massive

copper minerals.


Diorites

Diorites are a group of rocks composed essentially of a soda-lime felspar and

hornblende, embracing a wide range of types from acid to basic. Diorites were

formed by cooling far below the surface and occur in the Scottish Highlands,

the Channel Islands, California and other places.


Dolomite

Dolomite has the formulae CaMg(CO3)2 and a relative hardness of 4.

It's powder reacts vigorously with HCl. A potential ore of magnesium. Occurs in

widely extended rock masses as dolomitic limestone. Often intimately mixed with

calcite. Formed from ordinary limestone by the replacement of calcium by

magnesium.


Dumortierite

Dumortierite has the formulae Al7(BO3)(SiO4)3O3 and a relative hardness of 7.

It often has a bright colour and fibrous habit. Occurs in metamorphic rocks

rich in aluminum. Also in pegmatites and contact metamorphic rocks.


Dysodile

Dysodile is a yellow or green foliated mineral found in limestone.


Emerald

Emerald is a green precious stone variety of the mineral beryl.


Emery

Emery is an impure fine-grained aluminium oxide with the formulae Al2O3

employed widely as an abrasive. Typically emery consists of 60 percent corundum

and 40 percent iron oxide in the form of magnetite.


Enargite

Enargite has the formulae Cu3AsS4.

It has a relative hardness of 4.

It is a relatively rare mineral found in vein and replacement deposits

associated with pyrite, shpalerite, bornite, galena, chalcocite. Used as an ore

of copper.


Enstatite

Enstatite has the formulae Mg2Si2O6.

It has a relative hardness of 6.

It is a common and widespread mineral. Found in mafic plutonic and vocanic

rocks and often in both metallic and stony meteorites.


Epidote

Epidote has the formulae Ca2(Al,Fe)3Si3O12(OH).

It has a relative hardness of 7.

It is a common mineral. Found in regional and metamorphic rocks of mafic

composition and as a product of alteration of other minerals. Sometimes used as

a gemstone.


Epsomite

Epsomite has the formulae MgSO4ù7H2O.

It has a relative hardness of 3.

It has a bitter salty taste; dissolves easily in water. Occurs in delicate

fibrous and capillary aggregates. Often called 'epsom salt'. Found as an

efflorescent deposit on the walls of caves and sometimes in lake deposits.


Erythrite

Erythrite has the formulae Co3(AsO4)2ù8H2O.

It has a relative hardness of 3.

It often shows a vivid colour and occurs in thin crusts. An important indicator

of cobalt mineral deposits.


Euclase

Euclase has the formulae BeAlSiO4(OH).

It has a relative hardness of 8.

It is a variety of berly.




Feldspar

Feldspar refers to a group of minerals containing aluminum and silica. They all

show good cleavage in two directions at about 90 degrees. The hardness is about

6 and the specific gravity between 2.5 - 2.8.


Ferberite

Ferberite has the formulae FeWO4 - MnWO4.

It has a relative hardness of 6.

It is the chief ore of tungsten. A rare mineral found usually in pegmatite

dikes and high-temperature quartz veins associated with granite.


Ferruginous

Ferruginous refers to containing iron.


Figure-stone

see "Agalmatolit"


Fire-Garnet

see "Pyrope"


Flint

Flint is a compact mineral of fine grained silica. It is a variety of quartz.


Flow banding

Flow banding refers to a structure sometimes found in volcanic rocks where

alternating layers of rock have different mineral compositions.


Fluorapatite

Fluorapatite is a common mineral consisting of a mixed phosphate and flouride

of calcium. It is a source of phosphorus and was formerly used to make

phosphate fertiliser.


Fluorine

Fluorine is a non-metallic element occurring naturally.


Fluorite

Fluorite has the formulae CaF2.

It has a relative hardness of 4.

It is found in veins where it's the main mineral or with metallic ores,

especially lead and silver. Common in dolomites and limestone. Associated with

many different minerals. Used chiefly as a flux in the making of steel, also

for enameling, and it's used in the preparation of hydroflouric acid.


Fluorspar

Fluorspar is a natural mineral containing flourine.


Foliation

Foliation refers to a layered structure present in some metamorphic rocks which

results from the segregation of different minerals into roughly parallel layers.


Franklinite

Franklinite has the formulae (Zn,Mn,Fe)(Fe,Mn)2O4

It has a relative hardness of 7.

It is used as an ore of zinc and manganese. With minor exceptions, the mineral

is confined to Franklin, New Jersey.


Freibergite

Freibergite is a variety of tetrahedrite containing between 28 and 36 percent

silver.


Friable

Friable refers to crumbles or is pulverized easily.


Fulgurite

Fulgurite is a term applied to rocks whose surface has been melted by the

action of lightning, and on which the fused material has re-solidified as a

kind of thin coat or varnish.


Gabbros

Gabbros are basic rocks solidified under great pressure at considerable depths

in the earth's crust. They are coarse-grained and consist of plagioclase

felspar with augite. Sometimes the term is widely used to include similar rocks

composed of the same felspar with other minerals, and according to the minerals

contained they are known as norites, troctolites, eucrites, etc.


Gadolinite

Gadolinite (ytterbite) is a naturally occuring complex silicate containing

beryllium, iron and many of the rare earth metals, of which the latter is an

important source. The principal rare earths that occur in gadolinite are

yttrium and erbium, together with smaller amounts of cerium and lanthanum.


Galena

Galena (Lead Sulphide) is virtually the only source of lead and an important

ore of silver. It has the formulae PbS and a relative hardness of 3.

It is a very common metallic mineral. When found in veins that show a

connection to tigneous rocks, it is frequently found with silver minerals.

Galena is also found in limestones either as veins or as a replacement deposit.


Gannister

Gannister is a very siliceous close-grained variety of clay with a poor alkali

content found especially under coal seams in the Coal Measures of northern

England.


Garnet

Garnet has the formulae A3B2(SiO4)3.

It has a relative hardness of 8.

It is a widely distributed group with several minerals. Found in both

metamorphic and igneous rocks. Its chief use is as an inexpensive gem stone.

Much is used as an abrasive materal.


Garnierite

Garnierite has the formulae (Ni,Mg)6Si4O10(OH)8.

It has a relative hardness of 4.

It is an ore of nickel. It's probably formed as an alteration of nickel bearing

peridotites. Has a nice apple green colour.


Glauberite

Glauberite is a bitter salty tasting mineral that dissolves slowly in water. It

is a sedimentary mineral formed by the evaporation of saline water. It slowly

alters to gypsum when exposed to air. It has the formulae Na2Ca(SO4)2 and a

relative hardness of 3.


Glauconite

Glauconite is a mineral of marine origin and found in sedimentary deposits of

various kinds. Similar to a mineral called celadonite. Used in the textile,

sugar, and brewing industries; as a colouring agent and in the manufacture of

fertilizers. It has the formulae (K,Na)(Al,Fe,Mg)2(Al,Si)4O10(OH)2 and a

relative hardness of 2.


Glaucophane

Glaucophane is a sodium rich rock forming mineral which, like other amphiboles,

is poor in silica. It is of interest to petrologists in helping to define the

metamorphic conditions which formed the surrounding rock. It has the formulae

Na2(Mg,Fe)3Al2Si8O22(OH)2 and a relative hardness of 7. It often has a blue

colour.


Gneiss

Gneiss refers to a coarsely foliated (layered) metamorphic rock.


Goethite

Goethite is an ore of iron and a common mineral. Usually formed as a weathering

product of iron bearing minerals. The term "limonite" is commonly used for

earthy yellow and brown goethite. It has the formulae FeO(OH) and a relative

hardness of 6.


Gold

Gold is a rare element with the formulae Au and a relative hardness of 3

occuring in nature in widely distributed small amounts. The main source of gold

is in gold-quartz veins where gold was deposited from mineral bearing

solutions. When the veins weather, the gold is separated from the quartz and

mechanically settles on the stream floor as a placer deposit. Gold in jewellery

is measured in carats. 24 carat gold is pure, 22 carat gold is 22 parts gold to

2 parts other metals and so on.


Granite

Granite is a plutonic igneous rock containing a high proportion of silica.


Graphic tellurium

Graphic tellurium is an alternative name for Sylvanite.


Graphite

Graphite is pure carbon with a relative hardness of 2, often confused with the

heavier molybdenite. Formed from organic materials or by the presence of

hydrocarbons in a metamorphic region. Used in the manufacture of crucibles, as

a lubricant when mixed with oils, as 'lead' for pencils when mixed with clay.


Greasy

Greasy refers to a luster of a mineral which appears to be covered with thin

coat of oil.


Greenockite

Greenockite is the most common mineral containing cadmium but found in few

places and usually as an earthy coating on zinc ores. The largest use of

cadmium is for electroplating other metals to form chemical resistant coatings.

It has the formulae CdS and a relative hardness of 4.


Gypsum

Gypsum is a common mineral distributed in sedimentary rocks, often as thick

beds. Usually found under beds of rock salt as it's one of the first minerals

to crystallize from evaporated salt waters. Used in the production of plaster

of Paris. It has the formulae CaSO4ù2H2O and a relative hardness of 2.


Habit

Habit refers to the physical form of a crystal. It's determined by the shape

and relative proportions of the crystal faces.


Haematite

Haematite is an iron ore.


Halides

Halides refers to a group of minerals that are mostly compounds of halogen

elements (bromine, chlorine, flourine, iodine). Ex: halite, flourite.


Halite

Halite has the formulae NaCl.

It has a relative hardness of 3.

It is common salt. Tastes salty and exhibits lusterless cubic crystals.


Hardness

Hardness refers to hardness is the resistance of a smooth surface to

scratching. It's determined by the binding force of atoms within the crystal

structure. Moh's scale of hardness: 1)talc 2)gypsum 3)calcite 4)flourite

5)apatite 6)orthoclase 7)quartz 8)topaz 9)corundum 10)diamond.


Harmotome

Harmotome has the formulae (Ba,K)(Al,Si)2Si6O16ù6H20.

It has a relative hardness of 5.

It occurs mostly in volcanic rocks, especially basalt.


Hausmannite

Hausmannite has the formulae Mn2O4

It has a relative hardness of 6.

It is an excellent ore of manganese.


Hauyne

Hauyne has the formulae (Na,Ca)4-8(Al6Si6)O24(SO4,S)1-2.

It has a relative hardness of 6.

It is of interest to collectors. Occurs in igneous and volcanic rocks.


Hematite

Hematite has the formulae Fe2O3.

It has a relative hardness of 7.

It is the most abundant and important ore or iron. Has been found in enormous

deposits in the United States and elsewhere. Many samples are soft as the

hematite is sedimentary or weathered iron oxide and the true hardness is not

being measured.


Hemimorphite

Hemimorphite has the formulae Zn4Si2O7(OH)2ùH2O.

It has a relative hardness of 5.

It is an ore of zinc. Found in the oxidized regions of zinc deposits.


Heulandite

Heulandite has the formulae (Na,Ca)4-6Al6(Al,Si)4Si26O72ù24H2O.

It has a relative hardness of 4.

It is found in the cavities of basic igneous rocks and often associated with

calcite.


Hexagonal

Hexagonal refers to a six sided crystal with hexagonal bases. An unsharpened

pencil is a basic example.


Horn Silver

Horn Silver is a native chloride of silver, so called because when fused it

assumes a horny appearance.


Hornblende

Hornblende has the formulae (Ca,Na)2-3(Mg,Fe,Al)5(Al,Si)8O22(OH)2

It has a relative hardness of 6.

It is a common member of the amphibole group. Told from pyroxene by cleavage.

Found in igneous and metamorphic rocks.


Hydrothermal

Hydrothermal refers to the alteration of minerals or rocks by super-heated

mineral rich fluids, usually water, within a crystallizing magma.


Hydrozincite

Hydrozincite has the formulae Zn5(CO3)2(OH)6.

It has a relative hardness of 3.

It is found mainly in deposits associated with smithsonite and occurs as a

result of the oxidation of zinc bearing minerals. A major ore of zinc if found

in economic quantities.


Ilmenite

Ilmenite has the formulae FeTiO3.

It has a relative hardness of 6.

It has weak magnetism. The major ore of titanium and a common accessory mineral

in plutonic rocks. Also in metamorphic rocks. Occurs concentrated in black

sand. Associated with magnetite.


Intermediate rock

Intermediate rock refers to an igneous rock that is transitional between acidic

and basic rocks. Have a silica content between 54-65%.


Iron

Iron has the formulae Fe and a a relative hardness of 5.

It is is recovered primarily from iron bearing minerals and is recognizable by

the oxide coating on its surface (rust).


Isometric

Isometric refers to cubic. Three axis, all the same length and at right angles

to each other.


Jade

Jade is a group of glassy silicate minerals including jadetite and nephrite. It

is found in shades ranging from white to dark green in Asia.


Jadeite

Jadeite has the formulae Na(Al,Fe+3)Si2O6 and a relative hardness of 7.

It has long been prized in the Orient where it has been used to make beautiful

ornaments. Jadeite occurs in large masses in serpentine. Transparent and

translucent varieties are called jade.


Jasper

Jasper has the formulae SiO2 and a relative hardness of 7. It is a form of

quartz usually coloured red from inclusions of hematite.


Jet

Jet is a soft black mineral.


Kalmuck Agate

see "Cacholong"


Kaolinite

Kaolinite is a hydrous silicate of aluminium with the formulae Al2Si2O5(OH)4

and a relative hardness of 3.

It has a crumbly habit and forms the basis of most clay. Kaolinite is derived

from the decomposition of feldspars, particulary aluminum silicates and is one

of the most important of the natural industrial substances, used for bricks,

ceramics, and many other applications.


Kernite

Kernite has the formulae Na2B4O7ù4H2O and a relative hardness of 3.

It is a major ore of boron. Formed in playa lakes with the boron supplied by

thermal springs passing through the underlying volcanic rock.


Kimberlite

Kimberlite is an igneous rock containing very little silica.


Kyanite

Kyanite has the formulae Al2SiO5 and a relative hardness of 7.

It has a different hardness in two directions. An accessory mineral in gneiss

and mica schist. It often found with garnet and corundum. Used in the

production of refractory porcelains.


Labradorite

Labradorite has the formulae (Na,Ca)AlSi3O8 and a relative hardness of 6.

It is one of the plagioclase feldspars, also known as soda-lime feldspars.

Others in the grouping are: albite, oligoclase, andesine, bytownite, and

anorthite. Labradorite often has a beautiful display of colours. The name is

derived from the locality of Labrador.


Lamellar

Lamellar refers to composed of thin layers, scales, or plates


Lapis lazuli

Lapis lazuli is a blue mineral used in the manufacture of ultramarine pigment.


Lapis ollaris

see "Potstone"


Lapis-lazuli

Lapis-lazuli is a blue stone found in Iraq, Afghanistan and China.


Laumontite

Laumontite has the formulae Ca(Al2Si4)O12ù4H2O.

It has a relative hardness of 4.

It shows a powdery white surface. A form of anaclime (or analcite).

Characterized by the fact that it is monoclinic.


Lazulite

Lazulite has the formulae MgAl2(PO4)2(OH)2.

It has a relative hardness of 6.

It is a rare mineral and a minor gem stone. Usually found in quartzites

associated with kyanite, andalusite, corundum and rutile. Name derived from the

Arabic word for 'heaven' in regard to the mineral's colour.


Lazurite

Lazurite has the formulae (Na,Ca)8(Al,Si)12O24(S,SO4) and a relative hardness

of 5.

It is usually shows a deep blue colour. The greenish variety is called lapis

lazuli and is very rare. Lazurite is found in metamorphic limestones associated

with calcite and pyrite.


Lead Sulphide

see "Galena"


Lenticular

Lenticular refers to having a lens-like shape.


Lepidolite

Lepidolite has the formulae K(Li,Al)3(Si,Al)4O10(F,OH)2 and a relative hardness

of 4.

It is a relatively rare mineral found in pegmatic dikes and usually associated

with lithium bearing minerals such as pink and green tourmaline. Often found

intergrown with muscovite. Used as a source of lithium and it's used in the

manufacture of heat resistant glass.


Leucite

Leucite has the formulae KAlSi2O6.

It has a relative hardness of 6.

It is a rather rare mineral occuring only in igneous rocks and usually in

recent lavas. Found in rocks where the amount of silica in the magma was not

sufficient to form feldspar. It is not found, therefore, in rocks that contain

quartz. From the Greek word for 'white'.


Lime

Lime is the common name of calcium oxide.


Limestone

Limestone is a sedimentary rock composed of calcium carbonate.


Limonite

Limonite is an iron ore found in bog deposits. It has a relative hardness of

5.5.


Luster

Luster refers to the general look of a mineral in reflected light. Minerals are

divided into two types: metallic and non-metallic. There's no clear dividing

line between the two. In general, non-metallic minerals will transmit light

through a thin edge, are light coloured, and will have a light or colourless

streak. Non-metallic minerals are further described as: vitreous, resinous,

pearly, greasy, silky, adamantine.


Magma

Magma refers to molten rock beneath the earth's crust. It solidifies to form

igneous rocks.


Magnesite

Magnesite has the formulae MgCo3.

It has a relative hardness of 4.

It has been used as an ore of metallic magnesium but the primary source of

magnesium is sea water. Is a source of magnesia for industrial chemicals.

Commonly found in veins and masses derived from the alteration of serpentine

through the action of waters containing carbonic acid.


Magnetite

Magnetite has the formulae Fe3O4.

It has a relative hardness of 7.

It is the richest and most important ore of iron. Found as an accessory mineral

in most igneous rocks. Highly magnetic.


Malachite

Malachite has the formulae Ci2(CO3)(OH)2.

It has a relative hardness of 4.

It is a widely distributed copper ore. Found in the oxidized portions of copper

veins and is often associated with azurite, cuprite, native copper, iron

oxides, and sulphides of copper and iron. Often occurs in copper veins that are

found in limestone.


Manganite

Manganite has the formulae MnO(OH).

It has a relative hardness of 4.

It is strongly magnetic. An ore of manganese but seldom found in commercial

quantities. Often found in veins associated with granitic igneous rocks. Alters

to pyrolusite. Barite and calcite are frequent associates.


Marble

Marble is metamorphosed limestone.


Marcasite

Marcasite has the formulae FeS2.

It has a relative hardness of 7.

It often shows a white colour on a fresh surface. Found in iron metallic veins

and frequently with lead and zinc ores. Also found in sedimentary rocks.

Marcasite most frequently occurs as a replacement deposit in limestone and

often in concretions imbedded in clays, marls, and shales.


Margarite

Margarite has the formulae CaAl2(Al2Si2))O10(OH)2.

It has a relative hardness of 5.

It is a metamorphic mineral associated with staurolite and tourmaline.


Massive

Massive refers to a mineral that does not show any definite external crystal

form or consists of poorly defined masses of small crystals.


Mica

Mica refers to a group of silicate minerals having perfect cleavage in one

direction and which easily split into thin, elastic, sheets.


Microcrystalline

Microcrystalline refers to a rock in which the crystals are too small to be

seen without a microscope.


Microline

Microline has the formulae KAlSi3O8 and a relative hardness of 7. It has the

same composition as orthoclase but is distinguished by triclinic twinning

(usually requires a microscope). If a feldspar is a deep green it is microline

- and sometimes called 'amazon stone'. Told from plagioclase by lack of

striations.


Millerite

Millerite has the formulae NiS and a relative hardness of 4. It is the richest

ore of nickel but too scattered to be commercially important. Forms at low

temperatures often in cavities and as an altered form of other nickel minerals,

or as a crystal inclusion in other minerals.


Mimetite

Mimetite is a minor ore of lead and has the formulae Pb5(AsO4)3Cl and a

relative hardness of 4.

It is a relatively rare mineral which occurs in the oxidized portions of lead

bearing veins.


Mohs

Mohs is a scale of hardness applied to minerals. It ranges from 1 for talc to

diamond at 10.


Molybdates

Molybdates refers to a group of minerals in which the molybdate radical (MoO4)

is an important constituent. Ex: wulfenite


Molybdenite

Molybdenite has the formulae MoS2 and a relative hardness of 2. It is the main

ore of molybdenum. Resembles graphite but has a higher specific gravity and a

slight blue tint.


Monazite

Monazite has the formulae (Ca,La,Nd,Th)PO4 and a relative hardness of 6. It is

the chief ore of thorium and cerium. Thorium is a radioactive element. It is

concentrated in sand due to its durability and high specific gravity.

Associated with other heavy minerals such as magnetite, rutile, and zircon.


Monoclinic

Monoclinic refers to a crystal with six faces and three axes of unequal length.

Two axes are at right angles to each other and the third is inclined to the

plane of the other two. A ream of paper with a long edge sloped at an angle is

an example.


Moonstone

see "Adularia"


Mud

Mud is a mixture of clay, sand and organic matter.


Muscovite

Muscovite has the formulae KAl2(AlSi3)O10(OH)2 and a relative hardness of 3. It

has extremely perfect cleavage and thin flakes are flexible. Very common. Used

for electrical and heat insulation.


Natrolite

Natrolite has the formulae Na2(Al2Si3)O10ù2H2O and a relative hardness of 6. It

is of interest to collectors. Found lining cavities in basalts and other lavas.

Associated with calcite and zeolites.


Nephiline

Nephiline has the formulae (Na,K)AlSiO4 and a relative hardness of 6. It is

confined almost exclusively to the zinc deposits at Franklin, NJ. Associated

with franklinite and willemite, often in an intimate mixture.


Niccolite

Niccolite has the formulae NiAs and a relative hardness of 6. It is a minor ore

of nickel and often has a copper-like colour.


Nodular

Nodular refers to appearing as or composed of irregular lumps of rock or a

mineral.



Oligoclase

Oligoclase has the formulae (Na,Ca)AlSi3O8 and a relative hardness of 7. It is

a plagioclase feldspar. Of interest to petrologists and collectors. Varieties:

labradorite, anorthite.


Olivine

Olivine has the formulae (Mg,Fe)2SiO4 and a relative hardness of 7. It's name

is derived from the characteristic olive green colour. A common rock forming

mineral. A clear green variety is called peridot and has some uses as a gem.


Onyx

Onyx is a mineral formed of silica.


Opal

Opal has the formulae SiO2ùnH2O and a relative hardness of 6. It is found

lining and filling cavities in igneous and sedimentary rocks where it's been

deposited by hot waters. The ordinary varieties are common but the precious

varieties are quite valuable.


Orpiment

Orpiment has the formulae As2S3 and a relative hardness of 2. It is a rare

mineral usually associated with realgar. Used in dyeing but is poisonous.

Distinguished from sulphur by its perfect cleavage.


Orthoclase

Orthoclase has the formulae KAlSi3O8 and a relative hardness of 6. It is used

in the manufacture of porcelin and for other industrial purposes.


Orthorhombic

Orthorhombic refers to a rectangular crystal with three axes of different

lengths and all at right angles to each other. A closed book is a basic example.


Oxide

Oxide refers to a group of minerals where oxygen joined with a metal is a major

constituent.


Oxidized zone

Oxidized zone refers to the portion of an ore body that has been altered by

downward percolating groundwater and which contains dissolved oxygen and carbon

dioxide.


Pagodite

see "Agalmatolite"


Pearly

Pearly refers to a luster with the iridescent look of a pearl. Most commonly

seen on surfaces parallel to cleavage planes.


Pectolite

Pectolite has the formulae NaCa2Si3O8(OH) and a relative hardness of 5. It is

formed from hydrothermal solutions filling cavities in basalts. Associated with

zeolites, prehnite, calcite. Of interest to collectors.


Pegmatite

Pegmatite refers to an igneous rock of very coarse grain size. Usually found as

dikes within a larger rock mass. They are often excellent sources of fine

crystals.


Penninite

Penninite has the formulae Mg3(Si4O10)(OH)2ùMg3(OH)6 and a relative hardness of

3. It is a member of the chlorite group of minerals.


Pentlandite

Pentlandite has the formulae (Fe,Ni)9S8 and a relative hardness of 4. It is the

principal ore of nickel. The major use of nickel is in the manufacture of steel.


Perlite

A perlite is an obsidian, or other vitreous rock with a concentric structure

and which is expansible by heating.


Petalite

Petalite has the formulae LiAlSi4O10 and a relative hardness of 7. It is an ore

of lithium. Associated with spodumene, lepidolite, tourmaline.


Petroleum

Petroleum is a mineral oil from which petrol is derived.


Phenakite

Phenakite has the formulae Be2SiO4 and a relative hardness of 8. It is a rare

mineral found in pegmatite dikes associated with topaz, beryl, and apatite.

From the Greek word for 'a deceiver' in that it can be mistaken for quartz.


Phillipsite

Phillipsite has the formulae (K2,Na2Ca)(Al2Si4)O12ù4-5H2O and a relative

hardness of 5.

It is a hydrothermal mineral found lining cavities in basalt rocks associated

with chabazite. Formed as an alteration product of feldspars and volcanic ashes.


Phlogopite

Phlogopite has the formulae K(Mg,Fe)3(AlSi3)O10(F,OH)2 and a relative hardness

of 3.

It occurs as a result of the metamorphism of crystalline magnesium limestones

or dolomitic marbles. Also found in serpentine. Rarely found in igneous rocks.


Phosphates

Phosphates refers to a group of minerals where phosphate (PO4) is an important

constituent.


Pipe

Pipe refers to a cylindrical, vertical mass of igneous rock.


Placer

Placer refers to a concentrated deposit of mineral particles that have

weathered out of rock. Usually deposited by stream action.


Plagioclase

Plagioclase has the formulae Na(AlSi3O8) and a relative hardness of 6.

It is the plagioclase feldspar group includes: albite, oligoclase, andesine,

labradorite, bytownite, anorthite.


Playa

Playa refers to a shallow basin or plain in a desert where water collects after

a rain and then evaporates.


Plutonic rock

Plutonic rock refers to a granular igneous rock that has solidified at great

depth and shows a distinct grain structure. Ex: granite


Polybasite

Polybasite has the formulae (Ag,Cu)16SbS11 and a relative hardness of 3.

It is an ore of silver and resembles hematite but is much softer.


Polyhalite

Polyhalite has the formulae KaCa2Mg(SO4)4ù2H2O and a relative hardness of 4.

It is a source of potassium and occurs in bedded deposits associated with

sylvite, carnallite, halite, and has a characteristic red colour.


Potash

Potash is the name given to any mineral containing potassium.


Potassium argon dating

Potassium argon dating is a technique used in geology for estimating the age of

a mineral or rock, based upon the rate of decay of radioactive potassium into

argon.


Potstone

Potstone (Lapis ollaris) is a species of talc containing an admixture of

chlorite. It is green in colour and varys in shade, greasy and soft but hardens

on exposure to the air. It's English name comes from its capability to be

turned into vases and pots by turning.


Prase

Prase is a dark green variety of quartz, the colour being due to an admixture

of hornblende.


Precipitation

Precipitation refers to the process by which disolved or suspended solids are

separated from a liquid.


Prehnite

Prehnite has the formulae Ca2Al2Si3O10(OH)2 and a relative hardness of 7.

It occurs as a crusty lining in cavities in basalt and related rocks.

Associated with zeolites, datolite, pectolite, and calcite. Has a

characteristic green colour. Resembles hemimorphite but is of lower specific

gravity and fuses easily.


Proustite

Proustite has the formulae Ag3AsS3 and a relative hardness of 3.

It is an ore of silver. Has a characteristic ruby-red colour, vermilion streak

and a brilliant luster.


Pseudomorph

Pseudomorph refers to a mineral that has taken the outward crystal form of a

different mineral.


Psilomelane

Psilomelane has the formulae BaMnO16(OH)4 and a relative hardness of 6.

It is an ore of manganese. Usually occurs with pyrolusite. Different from other

manganese oxides in that it is of greater hardness and has an apparent lack of

crystal structure.


Pumice

Pumice is a light volcanic rock.


Purpurite

Purpurite has the formulae (Mn,Fe)PO4 .

It has a relative hardness of 5.

It is an alteration product of lithiophilite that occurs in pegmatites. Of

interest to collectors.


Pyragyrite

Pyragyrite has the formulae Ag3SbS3.

It has a relative hardness of 3.

It is an ore of silver. Similar to proustite but has a deeper red colour and is

less translucent. Forms in silver veins formed at low temperatures and is one

of the last minerals to crystallize in the process of deposition.


Pyrite

Pyrite has the formulae FeS2 and a relative hardness of 7.

It is iron pyrite. Formed from cooling magma. It is found as an igneous

segregation and also in metamorphic rocks and as vein deposits. Often found in

sedimentary rocks being both primary and secondary in origin. Often mined for

the gold or silver associated with it.


Pyrolusite

Pyrolusite has the formulae MnO2 and a relative hardness of 3.

It is the major ore of manganese which is used in the manufacture of steel.

Pyrolusite is formed when manganese is dissolved out of crystalline rocks and

then redeposited in dentrites etc.


Pyromorphite

Pyromorphite has the formulae Pb5(PO4)3Cl and a relative hardness of 4.

It is a minor ore of lead which is found in the oxidized portions of lead veins.


Pyrope

Pyrope (fire-garnet, Bohemian garnet) is a dark-red variety of garnet found

embedded in trap tufa in the mountains of Bohemia, and in serpentine in Germany.


Pyrophyllite

Pyrophyllite has the formulae A12Si4O10(OH)2 and a relative hardness of 2.

It is appears very similar to talc. A comparatively rare mineral found in

metamorphic rocks and often with kyanite.


Pyroxenes

Pyroxenes refers to a group of closely related and dark coloured rock forming

minerals. Ex: augite, diopside.


Pyrrhotite

Pyrrhotite has the formulae FeS and a relative hardness of 5.

It is a magnetic common mineral often found in igneous rocks. It is mined for

the nickel minerals associated with it.


Quartz

Quartz has the formulae SiO2 and a relative hardness of 7.

It is a very widespread mineral which occurs as an important constituent of

igneous rocks which have an excess of silica. Very resistant to mechanical and

chemical attack. Massive, fine grained types are called jasper, chert, flint,

agate. Coarse crystalline types called amethyst, rose quartz etc.


Realgar

Realgar has the formulae AsS and a relative hardness of 2.

It is found in veins of lead, silver, and gold ores associated with arsenic

minerals and stibnite. Also occurs as a deposit from hot springs. When mixed

with saltpeter and burned it gives a bright white light and was used in

fireworks.


Red Ochre

Red Ochre is a soft, earthy variety of haematite mineral.


Replacement

Replacement refers to the process by which one mineral is replaced by another

and the original physical form is often retained.


Resinous

Resinous refers to a luster with the appearance of resin.


Rhodochrosite

Rhodochrosite is an important manganese ore. In South America it is used as an

ornamental stone. It has a relative hardness of 4.


Rhodocrosite

Rhodocrosite has the formulae MnCO3.

It has a relative hardness of 5.

It is a minor ore of manganese. Occurs in veins with ores of silver, lead,

copper, and other manganese minerals.


Rhodonite

Rhodonite has the formulae (Mn,Fe,Mg)SiO3.

It has a relative hardness of 7.

It often has a pink-red colour. Sometimes polished for use as an ornamental

stone. Of interest to collectors.


Rhyolite

Rhyolite is a fine grained igneous rock.


Ruby

Ruby is the red transparent form of corundum. It is a precious stone.


Rutile

Rutile has the formulae TiO2.

It has a relative hardness of 7.

It exhibits a strong luster and often twinned crystals. Found in granite,

granite pegmatites, gneiss, mica schist, metamorphic limestone and dolomite.

Present as an accessory mineral in the rocks or in quartz veins. Name is

derived from the latin word "rutilus"; red.


Sanidine

Sanidine is a clear, glassy, often cracked variety of orthoclase felspar, which

is confined to modern volcanic rocks, such as trachyte, rhyolite and phonolite.


Sapphire

Sapphire is the blue transparent form of corundum.


Scapolite

Scapolite has the formulae (Na,Ca,K)4A13(Al,Si)3Si6O24(Cl,SO4,CO3) and a

relative hardness of 6.

It shows fluorescence. Occurs in the crystalline schists, gneisses, and often

is probably derived from the alteration of plagioclase feldspars. Also occurs

in crystalline limestones formed by metamorphic contact or igneous intrusion.

Associated with diopside, amphibole, garnet, apatite, and zircon.


Scheelite

Scheelite is an ore of tungsten. Found in granite pegmatites, contact

metamorphic deposits and high-temperature ore veins associated with granitic

rocks. Associated with cassiterite, topaz, flourite, apatite, molybdenite, and

wolframite. Sometimes found with gold.

It has the formulae CaWO4 and a relative hardness of 5.


Schist

Schist refers to a metamorphic rock which exhibits fine lamination or layers

along which the rock may be easily broken. Mica is a good example.


Schorl

Schorl is a rock compinded of quartz and black tourmaline. It is of igneous

origin and occurs associated with granite and crystalline schists. It has a

granular texture and is usually a grey colour.


Schwazite

Schwazite is a variety of Tetrahedrite containing upto 17 percent mercury.


Scolecite

Scolecite has the formulae Ca(Al2Si3)O10ù3H2O.

It has a relative hardness of 6.

It is of interest to collectors. Found in lavas and contact metamorphic

depostis.


Scorodite

Scorodite has the formulae FeAsO4ù2H2O.

It has a relative hardness of 4.

It is of interest to collectors. Occurs in the oxidized portions of metallic

veins as an alteration of arsenic containing minerals.


Secondary minerals

Secondary minerals refers to minerals formed by the alteration of preexisting

minerals.


Sepiolite

Sepiolite has the formulae Mg4Si6O15(OH)2ù6H2O.

It has a relative hardness of 3.

It is an alteration product of magnesite and serpentine. Becomes plastic when

mixed with water. Used in the manufacture of meerschaum pipes.


Serpentine

Serpentine has the formulae Mg6(Si4O10)(OH)8.

It has a relative hardness of 4.

It is a common mineral group and usually an alteration product of some

magnesium silicate, especially olivine, pyroxene, and amphibole. Frequently

associated with magnesite, chromite, and magnetite. Two varieties are

antigorite(massive) and chrysotile(fibrous; also called asbestos).


Shale

Shale is a fine black sedimentary rock.


Siderite

Siderite has the formulae FeCO3.

It has a relative hardness of 5.

It is becomes magnetic when heated. An ore of iron. Frequently found as an

impure admixture with clay materials. Also in concretions with concentric

layers.


Silica

Silica refers to silicon dioxide (SiO2). A very common mineral that is found in

many forms including quartz, opal, chert.


Silicates

Silicates refers to a group of minerals composed chiefly of SiO4. Ex: quartz,

orthoclase.


Silky

Silky refers to a silk-like luster on a mineral. Results from a fine, fibrous

and parallel surface.


Sillimanite

Sillimanite is a fibrous silicate with the formulae Al2SiO5.

It has a relative hardness of 7.

It is a somewhat rare mineral found as a constituent of gneiss and schist in

metamorhpic rocks. Often occurs with corundum.


Silver

Silver is a white, ductile metallic element that is sonorous, very malleable,

capable of a high degree of polish, and chiefly univalent with it's compounds

and has the highest thermal and electrical conductivity of any substance. It

has the symbol Ag.


Skutterudite

Skutterudite has the formulae CoAs2-3.

It has a relative hardness of 6.

It is an important ore of cobalt and nickel. Associated with native silver,

bismuth, calcite, arsenopyrite.


Slate

Slate is a metamorphic rock.


Smithsonite

Smithsonite has the formulae ZnCO3.

It has a relative hardness of 6.

It is an ore of zinc. Usually found with zinc deposits in limestone beds.


Soapstone

see "Steatite"


Sodalite

Sodalite has the formulae Na4Al3(SiO4)3Cl.

It has a relative hardness of 6.

It is usually has an attractive blue colour. Used as polished slabs and for

carved ornaments.


Sodium Tetraborate

see "Borax"


Specific gravity

Specific gravity refers to the relative density of a mineral. It is the ratio

of:; Weight in Air/(Weigth in Air - Weight in Water). ;This measurement is an

easily accomplished procedure using a simple balance or spring scale.


Sperrylite

Sperrylite is a rare natural compound of platinum and arsenic found in the

nickel mines of Sudbury in Canada. It has the formulae PtAs2 and a relative

hardness of 7.


Sphalerite

Sphalerite is the main ore of zinc. Associated with galena, pyrite, marcasite,

chalcopyrite, calcite. Formed as a replacement deposit in limestones and in

veins in igneous rocks. It has the formulae (Zn,Fe)S and a relative hardness of

4.


Sphene

Sphene (titanite, calcium silicate or titanate) is a source of titanium. A

rather common accessory mineral in igneous rocks. It is often found as crystals

and is commonly associated with chlorite. It has the formulae CaTiO(SiO4) and a

relative hardness of 6.


Spinel

Spinel is a common metamorphic mineral occuring imbedded in crystalline

limestone, gneisses, and serpentine. Occurs as a common accessory mineral in

many dark igneous rocks. When transparent and finely coloured it is used as a

gem. It has the formulae MgAl2O4 and a relative hardness of 8.


Spodumene

Spodumene is a source of lithium. Found occasionaly as very large crystals in

pegmatic dikes. It has the formulae LiAlSi2O6 and a relative hardness of 7.


Staurolite

Staurolite is an accessory mineral in crystalline schists, slates, and

sometimes gneisses. Often associated with garnet, kyanite, and tourmaline. May

form cross twins. It has the formulae (Fe,Mg,Zn)2Al9Si4O23(OH) and a relative

hardness of 8.


Steatite

Steatite (soapstone) is a variety of talc, hydrated magnesic silicate, usually

devoid of a distinct crystalline structure.


Stephanite

Stephanite is a minor ore of silver. One of the last minerals to form in silver

veins. It has the formulae Ag5SbS4 and a relative hardness of 3.


Stibnite

Stibnite is the major ore of antimony. It is Deposited by alkaline waters,

usually in association with quartz. Found in quartz veins or beds in granite

and gneiss. May occur as a replacement in limestones and shales.


Stilbite

Stilbite is a mineral of seconadary origin found in cavities in basalts and

related rocks. It has a relative hardness of 4.


Stone coal

see "Anthracite"


Strata

see "Stratum"


Streak

Streak refers to the colour of the powder produced when a mineral is rubbed

over the surface of a piece of unglazed, white porcelain.


Striations

Striations refers to very small parallel grooves or narrow channels of the

faces of a crystal.


Strontianite

Strontianite has the formulae SrCO3.

It has a relative hardness of 4.

It is source of strontium. Physically simialar to cerussite and witherite.

Associated with barite, celestite, and calcite in veins in limestone.

Occasionaly found in igneous rocks and as a gangue mineral in sulphide veins.


Sulphates

Sulphates refers to a group of minerals in which sulphate SO4 is an important

part.


Sulphides

Sulphides refers to a mineral group where sulphur is combined with one or more

metals.


Syenite

Syenite is a plutonic igneous rock consisting essentially of alkali-felspar and

one or more ferro-magnesian minerals, such as augite, hornblende, or mica.


Sylvanite

Sylvanite is a rare ore of gold, silver, and tellurium formed in low

temperature hydrothermal veins. It is associated with calaverite and other

tellurides - usually in quartz gangue.


Sylvite

Sylvite is an industrial mineral with a relative hardness of 2 used as a

fertilizer. Found in sedimentary evaporite deposits associated with halite.


Tachylite

Tachylite (Tachylyte) is a natural glass, formed by the rapid cooling of molten

basalt. It is a black or dark-brown and greasy looking substance. It is very

brittle and occurs in basaltic obsidians in dikes, veins and intrusive masses.


Tachylyte

see "Tachylite"


Talc

Talc has the formulae Mg3Si4O10(OH)2 and a relative hardness of 1.

It is a mineral of secondary origin formed by the alteration of magnesium

silicates. Usually found in metamorphic rocks where, in a non-crystalline form,

it occurs as 'soapstone' - and can make up large rock masses. Used for

laboratory table tops and for many industrial uses. It has a greasy feel.


Tenacity

Tenacity refers to the ability of a substance to resist being separated.


Tetragonal

Tetragonal refers to a crystal with four rectangular(not square) sides and two

square bases. A butter package is an example.


Tetrahedrite

Tetrahedrite has the formulae (Cu,Fe)12Sb4Si3 - (Cu,Fe)12As4S13.

It has a relative hardness of 5.

It is an ore of copper and silver. Commonly found in hydrothermal veins formed

at low to moderate temperatures. Usually associated with other silver, lead,

and copper minerals.


Thenardite

Thenardite has the formulae Na2SO4.

It has a relative hardness of 3.

It dissolves easily in water and has a weak salty taste. Forms in sedimentary

evaporite deposits in lakes and playas of desert climates. Used in the glass

and paper-making industries.


Till

A till is a stiff unstratified clay mixed with sand, gravel and boulders.


Tillite

A tillite is a rock composed of consolidated till.


Titanate

see "Sphene"


Titanite

see "Sphene"


Topaz

Topaz has the formulae Al2SiO4(F,OH)2.

It has a relative hardness of 8.

It is formed by flourine-bearing vapors given off during the last stages of the

solidification of igneous rocks. It is used as gem stone.


Torbernite

Torbenite is a uranium ore. It contains up to 61 percent uranium. It has a

relative hardness of 2.5.


Tourmaline

Tourmaline has the formulae (Na,Ca)(Al,Fe,Li,Mg)3A16(BO3)3(Si6O18) and a

relative hardness of 8.

It is most commonly found in granite pegmatites. It is usually black in colour,

but lighter coloured gem varieties are also found.


Trachyte

Trachyte is grey, yellow, brown, green and red volcanic rock consisting chiefly

of alkali felspar, and often containing crystals of glassy felspar, mica,

hornblende, or augite. Trachyte occurs in lava, intrusive sheets, and dykes

from the early Tertiary period.


Travertine

Travertine is a white or light-coloured crystalline concretionary limestone

deposited from springs and used for building.


Tremolite

Tremolite has the formulae Ca2Mg5Si8O22(OH)2 and a relative hardness of 6.

The fibrous variety has been used for asbestos. The compact variety is called

nephrite and is used for ornamental purposes in the orient. It is most often

found in impure limestones where the rock has recrystallized during

metamorphism.


Triclinic

Triclinic refers to a crystal with six faces as parallelograms and three axes

of unequal length all inclined to each other. An uncommon form of crystal.


Trydimite

Trydimite has the formulae SiO2 and a relative hardness of 7.

It is of interest to scientists and collectors due to its rarity.


Tufa

Tufa is a soft white porous rock of calcium carbonate deposited from solution

in spring water or percolating ground water.


Tuff

Tuff is rock debris consisting of volcanic ashes and igneous rocks of

fine-grained material.


Turquoise

Turquoise is a mineral of secondary origin usually found in small veins and

stringers. Used as a gem stone. It has a relative hardness of 6.


Twin

Twin refers to a mineral specimen comprised of two or more single crystals

intergrown in a systematic arrangement.


Ulexite

Ulexite is an ore of boron and is formed during the evaporation of lake basins.

It has a relative hardness of 2.


Umber

Umber is a naturally occurring mineral used as a pigment.


Uraninite

Uraninite is a radioactive important source of uranium. It occurs in pegmatites

and veins in granite; also as sedimentary deposits. It has a relative hardness

of 6.


Vanadinite

Vanadinite has the formulae Pb5(VO4)3Cl and a relative hardness of 3.

It is source of vanadium and a minor ore of lead. Found in the oxidized portion

of lead veins associated with other lead minerals. Vanadium is used as a

steel-hardening metal.


Vein

Vein refers to a sheetlike extension of mineral matter cutting through

preexisting rock.


Vermilion

see "cinnaba"


Vesicle

Vesicle refers to a small cavity in a volcanic rock.


Vesuvianite

Vesuvianite is usually found in crystalline limestones and is formed as a

result of contact metamorphism. It has the formulae

Ca10(Mg,Fe)2Al4(SiO4)5(SiO7)2(OH)4 and a relative hardness of 7.


Vitreous

Vitreous refers to a luster like that of glass. Quartz is an example.


Vivianite

Vivianite is a rare mineral of secondary origin, associated with pyrite in

copper and tin veins. Forms as a weathering product from primary iron-manganese

phosphates in pegmatites. Also found in beds of clay. It has a relative

hardness of 3.


Wavellite

Wavellite is a rare mineral of secondary origin. It is found frequently in

small amounts in crevices in aluminous, low-grade metamorphic rocks and in

limonite and phosphorite deposits. It has a relative hardness of 4.


Willemite

Willemite is an ore of zinc found in crystallized limestone and associated with

calcite, zincite, franklentie. It has a relative hardness of 6.


Witherite

Witherite is a somewhat rare mineral found most often in veins associated with

galena. It's a minor source of barium. It has the formulae BaCO3 and a relative

hardness of 4.


Woolastonite

Woolastonite has the formulae CaSiO3 and a relative hardness of 5. It is used

in the manufacture of tile. Occurs mainly as a contact metamorphic mineral in

crystalline limestones.


Wulfenite

Wulfenite has the formulae PbMoO4 and a relative hardness of 3. It often

displays brilliant colours and a tabular habit. It is a minor source of

molybdenum and is found in the oxidized portion of lead veins with other

secondary lead minerals.


Ytterbite

see "Gadolinite"


Zincite

Zincite has the formulae (Zn,Mn)O and a relative hardness of 5. It is an ore of

zinc and used in the production of zinc oxide.


Zircon

Zircon (zirconium silicate) has the formulae ZrSiO4 and a relative hardness of

8. It is a common accessory mineral found in all types of igneous rocks. When

transparent it's used as a gemstone.


Zoisite

Zoisite is a mineral formed in high temperature metamorphic rocks. It has the

formulae Ca2Al3(Si3O12)(OH) and a relative hardness of 7.

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