Rocks And Minerals (A-E)

Rocks And Minerals (A-E)


Accessory

Accessory refers to a mineral that occurs in a rock in minute quantities, and does not affect the way the rock is named or classified.

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. It has a relative hardness of 6. It commonly occurs in the crystalline schists, being often the chief constituent of green-coloured schists and greenstones. 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). It has a relative hardness of 4. It has brilliant fluorescence. Of scientific interest and much desired by collectors.

Aegirite

Aegirite has the formulae NaFe(Si2O6). It has 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.

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. It has 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). It has a relative hardness of 6. It occurs as a minor constituent of many igneous rocks. 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. It has a relative hardness of 4. It is usually formed by sulfuric acid solutions acting on rocks rich in alkalic feldspar. Used in the production of alum.

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.

Amygdule

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

Anaclime

Anaclime has the formulae NaAlSi2O6ù2H2O. It has a relative hardness of 6. It is of interest to collectors. Found in cavities of intrusive and volcanic igneous rocks; often as clear shiny crystals. Associated with calcite and zeolites.

Anatase

Anatase has the formulae TiO2. It has 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. Used as a coating of welding rods. A derivative it titanium.

Andalusite

Andalusite has the formulae Al2SiO5. It has a relative hardness of 8. It is formed by the metamorphism of aluminous shales and slate. Used in the manufacture of spark plugs and other porcelains. May serve as a gem stone if clear and transparent. Name from Andalusia, a province of Spain.

Andesine

Andesine has the formulae NaAlSi3O8. It has a relative hardness of 6.

Anglesite

Anglesite has the formulae PbSO4. It has a relative hardness of 3. It is a common, minor ore of lead. Formed by the oxidation of galena. Found in the upper, oxidzed portions of lead veins. Named after the Island of Anglesey.

Anhydrite

Anhydrite has the formulae CaSO4. It has a relative hardness of 4. It has rectangular cleavage fragments. Occurs in a manner similar to gypsum and often found with it but not as common. Found in the cap rock of salt domes and in limestone rocks. From the Greek meaning 'without water'.

Annivite

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

Anorthite

Anorthite has the formulae (Na,Ca)AlSi3O8. It has a relative hardness of 7. It is widely distributed and abundant rock-forming feldspar.

Anthophyllite

Anthophyllite has the formulae (Mg,Fe)7Si8O22(OH)2. It has a relative hardness of 6. It occurs in crystalline schists rich in magnesium. Of interest to collectors.

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 has the formulae Ag2S. It has a relative hardness of 3. It lacks distinct cleavage. 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.

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 has the formulae As. It has a relative hardness of 4. It has a garlicky odor; otherwise difficult to distinguish from antimony. A minor ore of arsenic and a relatively rare mineral found in veins in crystalline rocks associated with silver, cobalt, or nickel ores.

Arsenopyrite

Arsenopyrite has the formulae FeAsS. It has a relative hardness of 6. It 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.

Asbestos

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

Atacamite

Atacamite has the formulae Cu2Cl(OH)3. It has a relative hardness of 4. It is a comparatively rare copper mineral. Occurs in arid regions in the upper oxidized zone of copper deposits.

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 amphibole 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 sulfides.

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 has the formulae Be3Al2Si16O18. It has a relative hardness of 8. It has a characteristic six-sided outline. Used as a gem stone of various colours. It green variety is emerald. Beryl is also the major source of the rare element beryllium, a light metal similar to aluminum. Quite common and occurs usually in granite rocks, mica schists and with tin ores.

Biotite

Biotite has the formulae K(Mg,Fe)2(Al,Fe)Si3O10(OH,F)2. It has a relative hardness of 3. It is widely distributed rock forming mineral. Occurs in igneous and metamorphic rocks. A common member of the mica group.

Bismuth

Bismuth has the formulae Bi. It has a relative hardness of 3. It is the chief ore of bismuth and often shows broad cleavage surfaces. A somewhat rare mineral occurring in connection with ores of silver, cobalt, nickel, lead, and tin. Bismuth forms low melting alloys. It is used in fuses, medicine and cosmetics.

Bismuthinite

Bismuthinite has the formulae Bi2S3. It has 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. It has a relative hardness of 7. It occurs associated with beds of halite, anhydrite, and gypsum. 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 has the formulae Na2B4O7ù10H2O. It has a relative hardness of 3. It dissolves in water and has a sweetish alkaline taste. Formed as a deposit from the evaportation of salt lakes. Used in cleansing, antiseptic,, preservative, and chemical uses. Is a source of boron which is used in fuels.

Bornite

Bornite has the formulae Cu5FeS4. It has a relative hardness of 3. It is an ore of copper with a colourful tarnish(peacock). 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 has the formulae PbCuSbS3. It has a relative hardness of 3. It is an ore of lead, copper, and antimony which often exhibits twinned crystals. Occurs in in veins formed at moderate temperatures.

Brimstone

Brimstone is another name for sulphur.

Brookite

Brookite has the formulae à-TiO2. It has a relative hardness of 6. It is a source of titanium but deposits are usually too small to be of commercial use.

Brown Spar

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

Brucite

Brucite has the formulae Mg(OH)2. It has a relative hardness of 3. It is a decomposition product of magnesium silicates, especially serpentine. Variety: nemalite.

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.

Caliche

Caliche is naturally occurring sodium nitrate found in Chile.

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 has the formulae KMgCl3ù6H2O. It has a relative hardness of 3. It is a source of potassium coumpounds and magnesium. Has a bitter salty taste.

Carnelian

Carnelian is 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 sands, sandstones and around petrified trees. Probably formed as a deposition from meteoric waters. Strongly radioactive.

Cassiterite

Cassiterite has the formulae SnO2. It has a relative hardness of 7. It is the principal ore of tin. Widely distributed in small amounts but commerically available in only a few localities. Frequently associated with wolframite. Also found as rolled pebbles in placer deposits ('stream tin'). Usually found in veins associated with quartz, in or near granitic rocks.

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, sulfur, 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 has the formulae Ca(Al2Si4)O12ù6H2O. It has a relative hardness of 5. It is a mineral of secondary origin found lining cavities in volcanic and intrusive igneous rocks.

Chalcanthite

Chalcanthite has the formulae CuSO4ù5H2O. It has a relative hardness of 3. It dissolves quickly in water and produces a blue solution. A minor ore of copper and found only in arid regions. Occurs near the surface in copper veins. Often deposited on iron from the water in copper mines. Used in calico printing, insecticides and for industrial purposes.

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 has the formulae Cu2S. It has a relative hardness of 3. It is one of the most important copper ore minerals. It occurs primarily in enriched zones of sulfide deposits.

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.

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 sands 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.

Clinozoisite

Clinozoisite has the formulae Ca2Al3Si3O12(OH). It has a relative hardness of 7.

Cobaltite

Cobaltite has the formulae CoAsS. It has a relative hardness of 6. It is an ore of cobalt. 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 has the formulae Ca2B6O11ù5H2O. It has a relative hardness of 5. It is a major ore of boron. Occurs in high temperature hydrothermal veins or disseminated in metamorphic rocks associated with other cobalt and nickel sulfides/arsenides.

Columbite

Columbite has the formulae (Fe,Mn)(Nb,Ta)2O6. It has 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 has the formulae Cu. It has a relative hardness of 3. It is one of the essential metals of modern civilization. Native copper is found in copper veins but copper sulfides are the principal source ores of the metal.

Cordierite

Cordierite has the formulae Mg2Al4Si5O18. It has a relative hardness of 8. It 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.

Corundum

Corundum has the formulae Al2O3. It has a relative hardness of 9. It 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.

Covellite

Covellite has the formulae CuS. It has a relative hardness of 2. It has an indigo-blue colour. Not an abundant material but is found in most copper deposits, usually as a coating in the zone of sulfide enrichment.

Cristobalite

Cristobalite has the formulae SiO2. It has a relative hardness of 7. It 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.

Crocoite

Crocoite has the formulae PbCrO4. It has a relative hardness of 3. It 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. Name is Greek and means 'saffron', an allusion to the colour.

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. It has 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. It has a relative hardness of 5. It is found in the oxidation zone of copper deposits, in cavities of massive copper minerals.

Dolomite

Dolomite has the formulae CaMg(CO3)2. It has 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. It has 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.

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.