Olivine
Onyx
Opal
Orpiment
Orthoclase
Orthorhombic
Oxide
Oxidized zone
Pearly
Pectolite
Pegmatite
Penninite
Pentlandite
Perlite
Petalite
Petroleum
Phenakite
Phillipsite
Phlogopite
Phosphates
Pipe
Placer
Plagioclase
Platinum
Playa
Plutonic rock
Polybasite
Polyhalite
Potash
Potassium argon dating
Prase
Precipitation
Prehnite
Proustite
Pseudomorph
Psilomelane
Pumice
Purpurite
Pyragyrite
Pyrite
Pyrolusite
Pyromorphite
Pyrope
Pyrophyllite
Pyroxenes
Pyrrhotite
Quartz
Realgar
Red Ochre
Replacement
Resinous
Rhodochrosite
Rhodocrosite
Rhodonite
Rhyolite
Ruby
Rutile
Sanidine
Sapphire
Scapolite
Scheelite
Schist
Schorl
Schwazite
Scolecite
Scorodite
Secondary minerals
Sepiolite
Serpentine
Shale
Siderite
Silica
Silicates
Silky
Sillimanite
Silver
Skutterudite
Slate
Smithsonite
Sodalite
Specific gravity
Sperrylite
Sphalerite
Sphene
Spinel
Spodumene
Staurolite
Stephanite
Stibnite
Stilbite
Strata
Streak
Striations
Strontianite
Sulfates
Sulfides
Sulfur
Sulphides
Syenite
Sylvanite
Sylvite
Tachylite
Tachylyte
Talc
Tenacity
Tetragonal
Tetrahedrite
Thenardite
Till
Tillite
Topaz
Torbernite
Tourmaline
Trachyte
Travertine
Tremolite
Triclinic
Trydimite
Tufa
Tuff
Turquoise
Twin
Ulexite
Umber
Uraninite
Olivine has the formulae (Mg,Fe)2SiO4.
It has 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 is a mineral formed of silica.
Opal has the formulae SiO2ùnH2O.
It has 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 has the formulae As2S3.
It has 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 has the formulae KAlSi3O8.
It has a relative hardness of 6.
It is used in the manufacture of porcelin and for other industrial purposes.
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 refers to a group of minerals where oxygen joined with a metal is a major constituent.
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 refers to a luster with the iridescent look of a pearl. Most commonly seen on surfaces parallel to cleavage planes.
Pectolite has the formulae NaCa2Si3O8(OH).
It has 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 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 has the formulae Mg3(Si4O10)(OH)2ùMg3(OH)6.
It has a relative hardness of 3.
It is a member of the chlorite group of minerals.
Pentlandite has the formulae (Fe,Ni)9S8.
It has a relative hardness of 4.
It is the principal ore of nickel. The major use of nickel is in the manufacture of steel.
A perlite is an obsidian, or other vitreous rock with a concentric structure and which is expansible by heating.
Petalite has the formulae LiAlSi4O10.
It has a relative hardness of 7.
It is an ore of lithium. Associated with spodumene, lepidolite, tourmaline.
Petroleum is a mineral oil from which petrol is derived.
Phenakite has the formulae Be2SiO4.
It has 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 has the formulae (K2,Na2Ca)(Al2Si4)O12ù4-5H2O.
It has 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 has the formulae K(Mg,Fe)3(AlSi3)O10(F,OH)2.
It has 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 refers to a group of minerals where phosphate (PO4) is an important constituent.
Pipe refers to a cylindrical, vertical mass of igneous rock.
Placer refers to a concentrated deposit of mineral particles that have weathered out of rock. Usually deposited by stream action.
Plagioclase has the formulae Na(AlSi3O8).
It has a relative hardness of 6.
It is the plagioclase feldspar group includes: albite, oligoclase, andesine, labradorite, bytownite, anorthite.
Platinum has the formulae Pt.
It has a relative hardness of 5.
It is a rare metal and more valuable than gold. Has a high melting point and is resistant to chemicals.
Playa refers to a shallow basin or plain in a desert where water collects after a rain and then evaporates.
Plutonic rock refers to a granular igneous rock that has solidified at great depth and shows a distinct grain structure. Ex: granite
Polybasite has the formulae (Ag,Cu)16SbS11.
It has a relative hardness of 3.
It is an ore of silver. Resembles hematite but much softer.
Polyhalite has the formulae KaCa2Mg(SO4)4ù2H2O.
It has a relative hardness of 4.
It is urce of potassium. Occurs in bedded deposits associated with sylvite, carnallite, halite. Has a characteristic red colour.
Potash is the name given to any mineral containing potassium.
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 is a dark green variety of quartz, the colour being due to an admixture of hornblende.
Precipitation refers to the process by which disolved or suspended solids are separated from a liquid.
Prehnite has the formulae Ca2Al2Si3O10(OH)2.
It has 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 has the formulae Ag3AsS3.
It has a relative hardness of 3.
It is an ore of silver. Has a characteristic ruby-red colour, vermilion streak and a brilliant luster.
Pseudomorph refers to a mineral that has taken the outward crystal form of a different mineral.
Psilomelane has the formulae BaMnO16(OH)4
It has 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 is a light volcanic rock.
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 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 has the formulae FeS2.
It has 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 has the formulae MnO2.
It has 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 has the formulae Pb5(PO4)3Cl.
It has a relative hardness of 4.
It is a minor ore of lead which is found in the oxidized portions of lead veins.
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 has the formulae A12Si4O10(OH)2.
It has 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 refers to a group of closely related and dark coloured rock forming minerals. Ex: augite, diopside.
Pyrrhotite has the formulae FeS.
It has a relative hardness of 5.
It is magnetic. A common mineral often found in igneous rocks. It is mined for the nickel minerals associated with it.
Quartz has the formulae SiO2.
It has 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 has the formulae AsS.
It has 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 is a soft, earthy variety of haematite mineral.
Replacement refers to the process by which one mineral is replaced by another and the original physical form is often retained.
Resinous refers to a luster with the appearance of resin.
Rhodochrosite is an important manganese ore. In South America it is used as an ornamental stone. It has a relative hardness of 4.
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 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 is a fine grained igneous rock.
Ruby is the red transparent form of corundum. It is a precious stone.
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 is a clear, glassy, often cracked variety of orthoclase felspar, which is confined to modern volcanic rocks, such as trachyte, rhyolite and phonolite.
Sapphire is the blue transparent form of corundum.
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 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 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 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 is a variety of Tetrahedrite containing upto 17 percent mercury.
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 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 refers to minerals formed by the alteration of preexisting minerals.
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 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 is a fine black sedimentary rock.
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 refers to silicon dioxide (SiO2). A very common mineral that is found in many forms including quartz, opal, chert.
Silicates refers to a group of minerals composed chiefly of SiO4. Ex: quartz, orthoclase.
Silky refers to a silk-like luster on a mineral. Results from a fine, fibrous and parallel surface.
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 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 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 is a metamorphic rock.
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 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 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 has the formulae PtAs2.
It has a relative hardness of 7.
It is a rare natural compound of platinum and arsenic.
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 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 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 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 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 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 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 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.
see "Stratum"
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 refers to very small parallel grooves or narrow channels of the faces of a crystal.
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.
Sulfates refers to a group of minerals in which sulphate SO4 is an important part.
Sulfides refers to a mineral group where sulphur is combined with one or more metals.
Sulfur has the formulae S.
It has a relative hardness of 2.
It is formed near the crater rims of volcanoes by hot gases; also formed by the reduction of sulphates, especially gypsum.
Sulphides refers to a mineral group where sulphur is combined with one or more metals.
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 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 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 (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.
see "Tachylite"
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 refers to the ability of a substance to resist being separated.
Tetragonal refers to a crystal with four rectangular(not square) sides and two square bases. A butter package is an example.
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 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.
A till is a stiff unstratified clay mixed with sand, gravel and boulders.
A tillite is a rock composed of consolidated till.
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.
Torbenite is a uranium ore. It contains up to 61 percent uranium. It has a relative hardness of 2.5.
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 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 is a white or light-coloured crystalline concretionary limestone deposited from springs and used for building.
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 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 has the formulae SiO2.
It has a relative hardness of 7.
It is of interest to scientists and collectors due to its rarity.
Tufa is a soft white porous rock of calcium carbonate deposited from solution in spring water or percolating ground water.
Tuff is rock debris consisting of volcanic ashes and igneous rocks of fine-grained material.
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 refers to a mineral specimen comprised of two or more single crystals intergrown in a systematic arrangement.
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 is a naturally occurring mineral used as a pigment.
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.