The Amazing World of Minerals

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The Amazing World of Minerals
Photos www.johnbetts-fineminerals.com
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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
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Why are minerals important? Short Answer You
cant live without them!
Bauxite
Diamond
Cutting tools, getting married
Aluminum
Zeolites
Halite
Water purification, catalysts, medicine
Salt
Feldspar
Uraninite
Nuclear power, x-rays
Ceramics, porcelain
Borax
Quartz
Soap, cosmetics, fire retardant, fiberglass,
fertilizer, insecticide, airplanes, medicine!
Watches, radios, glass
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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

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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

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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
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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)
• Fingernail2.5 Penny3 Iron4-5
  Knife5.5 Glass6-7

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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 metallic
Quartz glassy
Talc Soapy, pearly
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Crystal Structure or Habit

• What shape is the crystal?
• Bladed Tabular Cube
• Dipyramidal Prism Rhombohedron
• Also descriptions like fibrous, platy, massive,
  equant, acicular are helpful

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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

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Density (mass/volume)

• Low Density High Density
• Halite Barite
• Graphite Galena

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Streak

• Many minerals leave a characteristic streak color
  when scratched across a porcelain plate
• Other minerals have no streak

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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

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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).

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Fluorescence
Diamond
Calcite
Selenite
Fluorite
Calcite with zincite
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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

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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 its orange/red and you eat it and it kills
  you it was probably Orpiment/Realgar

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Created by Nicolas Barth2007Geology
114AUniversity of California, Santa BarbaraSome
images herein borrowed from websites have not
been credited