Practical prospector's guide to minerals


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Practical prospector's guide to minerals

  1. 1. [PRACTICAL PROSPECTORS GUIDE TO MINERALS] October 3, 2012 PRACTICAL PROSPECTORS GUIDE TO MINERALS By Prof. Dr. Hassan Z. Harraz Geology Department Faculty Sciences, Tanta University-Egypt hharraz2006@yahoo.comOutline Topic 1:Rock-Forming Minerals Topic 2:Ores (Metallic) Topic 3:Ores (NON-Metallic) Topic 4:Industrial Minerals Topic 5:Gem Minerals1Page HZH, Tanta Univ
  2. 2. [PRACTICAL PROSPECTORS GUIDE TO MINERALS] October 3, 2012 PRACTICAL PROSPECTORS GUIDE TO MINERALS I- Rock-Forming Minerals Quartz  Most common mineral species  Vitreous luster; conchoidal fracture; hexagonal, prismatic crystals are diagnostic  Many color varieties: amethyst, smoky, rose, citrine  Uses: glass manufacture, abrasive, flux, optical instruments, electronics Feldspar Group Potassium feldspars: microcline, orthoclase, sanidine  blocky crystals, often show perthitic texture (especially microcline) Plagioclase feldspars: albite – anorthite series  range from white to black  often show play of colors (labradorescence)  striations on cleavage surface (albite twinning) Mica Group Muscovite (white mica) Biotite (black mica) Phlogopite (brown mica) Sericite (brown to buff mica) Lepidolite (purple mica)  lithium-rich pegmatites  micaceous cleavage, elastic nature of plates and hardness distinguish micas from all other sheet-like minerals such as talc, gypsum and brucite Pyroxene Group  Generally green to black (except spodumene, which can be white, yellowish, pink or green).  2 good to perfect cleavages at nearly right angles (chief distinguishing  characteristic between pyroxenes and amphiboles).  Pyroxenes are common in mafic to ultramafic rocks and in skarns  Emerald-green diopside (chrome-diopside) is a diamond indicator mineral  Spodumene is a lithium pyroxene found in rare-element pegmatites  Jadeite is one of the "true" jades and is a pyroxene Amphibole Group • Generally green to black (some, like tremolite, are white)2Page HZH, Tanta Univ
  3. 3. [PRACTICAL PROSPECTORS GUIDE TO MINERALS] October 3, 2012  2 good to perfect cleavages at 56 and 124 degrees (chief distinguishing  characteristic between amphiboles and pyroxenes).  BC jade is "nephrite", a variety actinolite, and is considered a "true" jade.  amphiboles are common in skarns and in fairly high-grade metamorphic rocks. Garnet Group Almandine (iron – aluminum garnet)  generally red  found in schists Pyrope (magnesium – aluminum garnet)  generally red  diamond indicator mineral (kimberlites, lamprophyres) Spessartine (manganese – aluminum garnet)  red to orange  most often in rare-element pegmatites Grossular (calcium – aluminum garnet)  brown, green, red, yellow  often found in skarns  gem brown variety known as "hessonite" Andradite (calcium – iron garnet)  brown, green, red, yellow, black  often found in skarns  gem green variety could be "demantoid"  titaniferous variety (black) is known as "melanite" Uvarovite (calcium – chromium garnet)  chrome green  associated with altered ultramafic rocks. Serpentine Group  varied green color, greasy luster, often fibrous (or splintery) Olivine  vitreous luster, conchoidal fracture, green color, presence in basalt as nodules Carbonate Group Calcite  3 cleavages not at right angles  fizzes readily with weak acid Siderite  typical carbonate cleavage  light to dark brown Dolomite  curved, rhombohedral crystals  white, pink, gray3Page HZH, Tanta Univ
  4. 4. [PRACTICAL PROSPECTORS GUIDE TO MINERALS] October 3, 2012II- Ores (Metallic)A. GoldB. Platinum Group Elements:  Platinum, Palladium, Iridium, Osmium  placer deposits, ultramafic rocksC. Native Silver  wires in pockets, hackly fracture, tarnishes black  often as an impurity in galenaD. Sulfosalts  Pyrargyrite/Proustite (ruby silvers)  Stephanite  TetrahedriteE. Native Copper (100% Cu)  often in basalt; sometimes in oxidized zone; hackly fracture, copper colorF. Chalcopyrite (35% Cu)  no cleavage, greenish-black streak, slightly greener yellow than pyriteG. Bornite (63% Cu)  purple-blue iridescent tarnish, BRONZY on FRESH SURFACEH. Covellite (66% Cu)  ELECTRIC BLUE, platy cleavageI. Chalcocite (79% Cu)  black, SECTILEJ. Galena  3 perfect CLEAVAGES at right angles, DENSITY, lead-gray color  secondary lead minerals: anglesite, cerussite, pyromorphiteJ. Molybdenite  chief ore of molybdenum  SOFT, slightly bluer-gray than graphite (compare it with a pencil ‘lead’)L. Pyrite  often in good crystals (pyritohedra, cubes, octahedra); brittle, black streakM. Arsenopyrite  no cleavage, "garlic" smell sometimes when brokenN. Pyrrhotite  bronzy color, sometimes magneticO. Stibnite  main ore of antimony.  elongate crystals that are often ‘bent’; ONE PERFECT CLEAVAGE and lower density distinguish it from galena.  will easily melt in a candle flameP. Graphite  SOFT, black (like pencil "lead")4Page HZH, Tanta Univ
  5. 5. [PRACTICAL PROSPECTORS GUIDE TO MINERALS] October 3, 2012III- Ores (NON-Metallic)A. Sphalerite  resinous to sub-metallic luster  yellow to green to red to black  Important ore of cadmium as well  alters to smithsonite, hydrozincite (fluorescent)B. Wolframite  HEAVY, reddish to black, tabular crystals with one perfect cleavageC. Scheelite  White to brown, fluoresces bluish whiteD. Manganese Oxides  psilomelane is a mixture of compact manganese oxides; mixture of earthy manganese oxides is known as wad.  black, soft (often show dendritic stains)E. Iron Oxides  mixture of iron oxides is generally known as limonite 1. Hematite: red-brown streak 2. Goethite: brown streakF. Magnetite  black, dense, MAGNETICG. Cassiterite  black; glassy to resinous lusterH. Cinnabar  red; bright red streak; softI. Cuprite  red, often associated with malachite or other secondary copper mineralsJ. Malachite/Azurite  both are alteration products of other copper minerals  (MALACHITE is GREEN; AZURITE is BLUE (‘azure-blue’, in fact)5Page HZH, Tanta Univ
  6. 6. [PRACTICAL PROSPECTORS GUIDE TO MINERALS] October 3, 2012IV- Industrial MineralsDiamond  as adamantine crystals in kimberlite or lamprophyre  placer deposits (weathered kimberlites/lamprophyres)Sulfur  as a native element in sedimentary rocks (often associated with petroleum)Barite  one to two good cleavages, VERY heavy  in hydrothermal veins and sedimentary exhalative depositsGypsum  white to gray, softness is characteristic  sedimentary rocksMagnesite  generally white  found most commonly in sedimentary rocks, but also in carbonatites  hydromagnesite and epsomite are evaporites found in playa lakes (from the alteration of volcanic rocks)Apatite  hexagonal crystals, many colors  found in many environments  distinguished from beryl by its hardness (beryl cannot be scratched by a knife)Zeolite Group  generally white or off-white  found in volcanic rocks or low grade metamorphic rocks  economic deposits found as beds of altered volcanic ash  "boil" when torchedFluorite  four directions of perfect CLEAVAGECorundum  HARDNESS of 96Page HZH, Tanta Univ
  7. 7. [PRACTICAL PROSPECTORS GUIDE TO MINERALS] October 3, 2012V- Gem MineralsThe following are reasonable to be expected, or have already been found in BritishColumbia.Corundum  Ruby: red corundum coloured by chromium  Sapphire: BLUE, green, pink, yellow, colourless corundum coloured by iron and/or titaniumDiamondBeryl  hexagonal cross-section; prismatic to tabular crystals; generally in pegmatitesVarieties of Beryl:  Aquamarine: blue to green beryl coloured by iron  Emerald: green beryl coloured by chromium or vanadium  Goschenite: colourless beryl (originally cesium-bearing beryl)  Heliodor: yellow beryl coloured by ironTourmaline  diamond-shape cross-section; perfect basal cleavage (perpendicular to the length of the crystal)Varieties of Gemmy Tourmaline:  Schorl: black tourmaline found in simple pegmatites, hydrothermal veins and metamorphic rocks  Elbaite: lithium-bearing tourmaline found almost exclusively in pegmatites;  Rubellite (pink), Verdelite (green), Indicolite (blue), Achroite (colourless)  Liddicoatite: another lithium-bearing tourmaline, again in pegmatitesTopaz  diamond-shape cross-section; perfect basal cleavage (perpendicular to the length of the crystal)Garnet  metamorphic rocks; pegmatitesVarieties of Gemmy Garnet:  Grossular: gem brown variety is hessonite  Andradite: gem green variety is demantoid  Spessartine: bright orange is best qualityQuartzVarieties of Quartz:  Amethyst: purple quartz coloured by iron (Fe4+)  Citrine: yellow/orange quartz coloured by iron  Smoky Quartz: brown to black quartz affected by radiation  Rose Quartz: pink quartz coloured by manganese7Page HZH, Tanta Univ
  8. 8. [PRACTICAL PROSPECTORS GUIDE TO MINERALS] October 3, 2012  Chalcedony: cryptocrystalline quartz; gray, greasy to silky luster; found in volcanic rocks and some sedimentary rocks  Agate: concentrically banded chalcedony; variously coloured  Onyx: flat, layered chalcedony; usually black/white or red/white<  Carnelian: chalcedony coloured red by iron  Chrysoprase: chalcedony coloured green by nickel  Jasper: chalcedony coloured red, green, yellow or black by iron oxideOpal  in volcanic and sedimentary rocks  common versus precious opal8Page HZH, Tanta Univ