Minerals in geology 3

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The Amazing World of Minerals Photos: www.johnbetts-fineminerals.com Cueva de los cristales, Naica Mine, Mexico • • • • • • Series of gypsum filled caves found at 950ft depth in a mine 122ºF!! 100% humidity!! Explorers and scientists must wear refrigerated space suits to avoid being boiled alive Even with the suits they can only remain in the caves for 10 minutes Gypsum seems to have formed in unusually saturated geothermal fluids associated with a nearby fault Exploration continues today Photos: La Venta Exploring Team Why are minerals important? Short Answer: You can’t live without them! Bauxite Aluminum Diamond Cutting tools, getting married Halite Zeolites Salt Water purification, catalysts, medicine Feldspar Ceramics, porcelain Quartz Watches, radios, glass Uraninite Nuclear power, x-rays Borax Soap, cosmetics, fire retardant, fiberglass, fertilizer, insecticide, airplanes, medicine! Uses of minerals in geology Determining • Ages of rocks • Tectonic environment • Compositions of source magma • Pressure and temperature histories of rocks • Reaction rates • Past strain recorded in rocks • Paleomagnetism • Economic ores • The chemical make-up of the Earth and how elements are exchanged Mineral Identification • Since every mineral is chemically and structurally unique, every mineral has properties that can be used to distinguish it from other minerals • A major purpose of this class will be give you the confidence to identify minerals in the field so you can use them to answer geological questions Common Properties for Mineral Identification • Color- many minerals have a characteristic color – Ex: Epidote is almost always green – Ex: Sulfur is almost always yellow • However, minerals such as quartz, tourmaline and garnet can be virtually any color Quartz Garnet Tourmaline Hardness • Most used method is the Mohs Scale • 1)Talc 2) Gypsum 3) Calcite 4) Fluorite 5) Orthoclase 6) Apatite 7) Quartz 8) Topaz 9) Corundum 10) Diamond • Minerals with a lower number will be scratched by minerals with a higher number • Mohs scale is relative (diamond is 10x harder than corundum) • Fingernail=2.5 Penny=3 Iron=4-5 Knife=5.5 Glass=6-7 Luster • A description of the way light interacts with the surface of a mineral or rock • Luster descriptions include metallic, earthy, waxy, greasy, glassy, silky, brilliant, dull, satin spar, soapy Pyrite Quartz Talc metallic glassy Soapy, pearly Crystal Structure or Habit • What shape is the crystal? Bladed Tabular Dipyramidal Prism Cube Rhombohedron Also descriptions like fibrous, platy, massive, equant, acicular are helpful Cleavage and Fracture • Cleavage occurs along specific planes of weakness in a mineral These planes are caused by the molecular structure of the mineral • Crystals with good cleavage like calcite or mica will always break parallel to the same plane • Number, quality and angular relationships between cleavage planes are important • Minerals with no cleavage like quartz will fracture – Conchoidal or uneven Density (mass/volume) • Low Density High Density Halite Barite Graphite Galena Streak • Many minerals leave a characteristic streak color when scratched across a porcelain plate • Other minerals have no streak Mineral Assemblages/Tectonic Environment • Minerals commonly occur with other characteristic minerals – Ex: Scarn minerals: Epidote, Calcite, Garnet, Scheelite – Ex: Hydrothermal sulfide deposits: Galena, Barite, Sphalerite, Pyrite, Fluorite, Calcite – Ex: Pegmatites: Tourmaline, Quartz, Lepidolite, Beryl, Muscovite, Feldspar • Some minerals occur in specific environments – Ex: Zeolite minerals commonly grow in vesicles in igneous rocks – Ex: Evaporites commonly occur in desert playas Fluorescence • Some minerals glow in the presence of either short or long wave ultraviolet light There are several minerals that exhibit this property some of which are calcite, diamond, fluorite, halite, scheelite and willemite • Fluorescence occurs on the atomic level in a mineral The electrons of an atom each have a certain energy level called their 'ground state' (blue electrons) • In fluorescent minerals, energy is absorbed by the atom increasing the energy of the electrons, causing them to jump to the next energy level (red electrons) • This increase in energy level does not last long (approximately 10-8 seconds) When the electrons fall back to their ground state, the extra energy is emitted from the atom in the form of visible light (green sparkles) Fluorescence Diamond Calcite Selenite Fluorite Calcite with zincite Other Properties used for ID • Optical Properties – Ulexite- fiber optic properties – Calcite- double refraction – Optical Microscopy • HCl Acid – Calcite- fizzes when acid is applied • Twinning – Orthoclase feldspar- Carlsbad twinning – Plagioclase- Albite twinning Other Properties used for ID • Magnetism – Magnetite- magnetic • Smell – Sulfur- rotten eggs • Alteration/Weathering – Hematite- rusts red – Olivine- alters to orange mineral called iddingsite • Taste – Halite- salt – If it’s orange/red and you eat it and it kills you it was probably Orpiment/Realgar Created by Nicolas Barth 2007 Geology 114A University of California, Santa Barbara Some images herein borrowed from websites have not been credited [...]... Many minerals leave a characteristic streak color when scratched across a porcelain plate • Other minerals have no streak Mineral Assemblages/Tectonic Environment • Minerals commonly occur with other characteristic minerals – Ex: Scarn minerals: Epidote, Calcite, Garnet, Scheelite – Ex: Hydrothermal sulfide deposits: Galena, Barite, Sphalerite, Pyrite, Fluorite, Calcite – Ex: Pegmatites: Tourmaline,... Tourmaline, Quartz, Lepidolite, Beryl, Muscovite, Feldspar • Some minerals occur in specific environments – Ex: Zeolite minerals commonly grow in vesicles in igneous rocks – Ex: Evaporites commonly occur in desert playas Fluorescence • Some minerals glow in the presence of either short or long wave ultraviolet light There are several minerals that exhibit this property some of which are calcite, diamond,... and willemite • Fluorescence occurs on the atomic level in a mineral The electrons of an atom each have a certain energy level called their 'ground state' (blue electrons) • In fluorescent minerals, energy is absorbed by the atom increasing the energy of the electrons, causing them to jump to the next energy level (red electrons) • This increase in energy level does not last long (approximately 10-8... from the atom in the form of visible light (green sparkles) Fluorescence Diamond Calcite Selenite Fluorite Calcite with zincite Other Properties used for ID • Optical Properties – Ulexite- fiber optic properties – Calcite- double refraction – Optical Microscopy • HCl Acid – Calcite- fizzes when acid is applied • Twinning – Orthoclase feldspar- Carlsbad twinning – Plagioclase- Albite twinning Other Properties... magnetic • Smell – Sulfur- rotten eggs • Alteration/Weathering – Hematite- rusts red – Olivine- alters to orange mineral called iddingsite • Taste – Halite- salt – If it’s orange/red and you eat it and it kills you it was probably Orpiment/Realgar Created by Nicolas Barth 2007 Geology 114A University of California, Santa Barbara Some images herein borrowed from websites have not been credited
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