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) and a relative hardness of 4.
It has brilliant fluorescence. Of scientific interest and much desired by collectors.

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.

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).
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 sulphuric 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 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 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 is a metal
element with the symbol As and a relative hardness of 4.
It has a garlicky odor; 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.

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 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.

Bismuth
Bismuth is a metal
element with the symbol Bi and a relative hardness of 3. Bismuth is a somewhat rare mineral occurring in connection with ores of silver, cobalt, nickel, lead, and tin. Bismuth forms low melting alloys and is used in fuses, medicine and cosmetics.

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 has the formulae Na2B4O710H2O and a relative
hardness of 3. It dissolves in water and has a sweetish alkaline taste. It is formed as a deposit from the evaportation of salt lakes and is used in cleansing, antiseptic,, preservative, and chemical uses. Borax is also a source of boron which is used in fuels.

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

Cassiterite
Cassiterite has the formulae SnO2 and 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, 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 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 sulphide 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 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 has the formulae
Cu and a relative hardness of 3.
It 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.

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 sulphide 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 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.