*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. Cloth was made of it by the ancient Egyptians. 
*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
#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
#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
#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
#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
#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. 
*Fire-Garnet
#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 has the formulae Na2Ca(SO4)2.
It has a relative hardness of 3.
It has a bitter salty taste; dissolves slowly in water. Is a sedimentary mineral formed by the evaporation of saline water. Slowly alters to gypsum when exposed to air. 
*Glauconite
Glauconite has the formulae (K,Na)(Al,Fe,Mg)2(Al,Si)4O10(OH)2
It has a relative hardness of 2.
It is 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.
*Glaucophane
Glaucophane has the formulae Na2(Mg,Fe)3Al2Si8O22(OH)2.
It has a relative hardness of 7.
It often has a blue colour. A sodium rich rock forming mineral which, like other amphiboles, is poor in silica. Of interest to petrologists in helping to define the metamorphic conditions which formed the surrounding rock.
*Gneiss
Gneiss refers to a coarsely foliated (layered) metamorphic rock. 
*Goethite
Goethite has the formulae FeO(OH).
It has a relative hardness of 6.
It 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. 
*Gold
Gold has the formulae Au.
It has a relative hardness of 3.
It is a rare element but occurs 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. 
*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 has the formulae C.
It has a relative hardness of 2.
It is pure carbon and 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. Feels greasy.
*Greasy
Greasy refers to a luster of a mineral which appears to be covered with thin coat of oil.
*Greenockite
Greenockite has the formulae CdS.
It has a relative hardness of 4.
It 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.
*Gypsum
Gypsum has the formulae CaSO4ù2H2O.
It has a relative hardness of 2.
It 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. 
*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.
It has a relative hardness of 5.
It is is recovered primarily from iron bearing minerals. Iron is recognizable by the oxide coating on its surface.
*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.
It has a relative hardness of 7.
It is long prized in the Orient where its been used to make beautiful ornaments. Occurs in large masses in serpentine. Transparent and translucent varieties are called jade.
*Jasper
Jasper has the formulae SiO2.
It has 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. 
*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.
It has 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-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).
It has a relative hardness of 5.
It is usually shows a deep blue colour. The greenish variety is called lapis lazuli and is very rare. Found in metamorphic limestones associated with calcite and pyrite.
*Lead Sulphide
#Galena
*Lenticular
Lenticular refers to have a lens-like shape. 
*Lepidolite
Lepidolite has the formulae K(Li,Al)3(Si,Al)4O10(F,OH)2.
It has 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. 
*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. 
*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. 
*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 has the formulae Ag.
It has a relative hardness of 3.
It is native silver results from the deposition of silver from hydrothermal solutions. Most of the world's silver comes from silver ores rather than pure native silver.
*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. 
*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.
*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 has the formulae PtAs2.
It has a relative hardness of 7.
It is a rare natural compound of platinum and arsenic. 
*Sphalerite
Sphalerite has the formulae (Zn,Fe)S.
It has a relative hardness of 4.
It 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.
*Sphene
Sphene has the formulae CaTiO(SiO4).
It has a relative hardness of 6.
It is a source of titanium. A rather common accessory mineral in igneous rocks. Often found as crystals. Commonly associated with chlorite.
*Spinel
Spinel has the formulae MgAl2O4.
It has a relative hardness of 8.
It 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.
*Spodumene
Spodumene has the formulae LiAlSi2O6.
It has a relative hardness of 7.
It is a source of lithium. Found occasionaly as very large crystals in pegmatic dikes.
*Staurolite
Staurolite has the formulae (Fe,Mg,Zn)2Al9Si4O23(OH).
It has a relative hardness of 8.
It is an accessory mineral in crystalline schists, slates, and sometimes gneisses. Often associated with garnet, kyanite, and tourmaline. May form cross twins. 
*Stephanite
Stephanite has the formulae Ag5SbS4.
It has a relative hardness of 3.
It is a minor ore of silver. One of the last minerals to form in silver veins. 
*Stibnite
Stibnite has the formulae Sb2S3.
It has a relative hardness of 2.
It is the major ore of antimony. 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 has the formulae NaCa2(Al5Si13)O36ù14H2O.
It has a relative hardness of 4.
It is a mineral of seconadary origin found in cavities in basalts and related rocks. 
*Strata
#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 has the formulae AgAuTe4.
It has a relative hardness of 2.
It is a rare ore of gold, silver, and tellurium. Formed in low temperature hydrothermal veins. Associated with calaverite, other tellurides - usually in quartz gangue. 
*Sylvite
Sylvite has the formulae KCl.
It has a relative hardness of 2.
It is an industrial mineral 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
#Tachylite 
*Talc
Talc has the formulae Mg3Si4O10(OH)2.
It has 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. 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. 
*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)
It has a relative hardness of 8.
It is most commonly found in granite pegmatites. Usually black 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.
It has a relative hardness of 6.
It is the fibrous variety has been used for asbestos. The compact variety is called nephrite and is used for ornamental purposes by oriental people. 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.
It has 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 has the formulae CuAl6(PO4)4(OH)8ù5H2O and a relative hardness of 6.
It is a mineral of secondary origin usually found in small veins and stringers. Used as a gem stone.
*Twin
Twin refers to a mineral specimen comprised of two or more single crystals intergrown in a systematic arrangement. 
*Ulexite
Ulexite has the formulae NaCaB5O9ù8H2O and a relative hardness of 2.
It is an ore of boron and is formed during the evaporation of lake basins.
*Umber
Umber is a naturally occurring mineral used as a pigment.
*Uraninite
Uraninite has the formulae UO2 and a relative hardness of 6.
It is radioactive. An important source of uranium. Occurs in pegmatites and veins in granite; also as sedimentary deposits. 
*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
#cinnaba 
*Vesicle
Vesicle refers to a small cavity in a volcanic rock. 
*Vesuvianite
Vesuvianite has the formulae Ca10(Mg,Fe)2Al4(SiO4)5(SiO7)2(OH)4 and a relative hardness of 7.
It is usually found in crystalline limestones and is formed as a result of contact metamorphism. 
*Vitreous
Vitreous refers to a luster like that of glass. Quartz is an example.
*Vivianite
Vivianite has the formulae Fe3(PO4)2ù8H2O and a relative hardness of 3.
It 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.
*Wavellite
Wavellite has the formulae Al3(PO4)2(OH)3ù5H2O and a relative hardness of 4.
It is a rare mineral of secondary origin. Found frequently in small amounts in crevices in aluminous, low-grade metamorphic rocks and in limonite and phosphorite deposits. 
*Willemite
Willemite has the formulae Zn2SiO4 and a relative hardness of 6.
It is an ore of zinc. Found in crystallized limestone. Associated with calcite, zincite, franklentie. 
*Witherite
Witherite has the formulae BaCO3 and a relative hardness of 4.
It is a somewhat rare mineral found most often in veins associated with galena. It's a minor source of barium.
*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. A minor source of molybdenum. Found in the oxidized portion of lead veins with other secondary lead minerals. 
*Ytterbite
#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 has the formulae Ca2Al3(Si3O12)(OH) and a relative hardness of 7.
It is formed in high temperature metamorphic rocks.
