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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
Halite
Salt
Diamond
Cutting tools, getting married
Feldspar
Ceramics, porcelain
Quartz
Watches,
radios, glass
BoraxSoap, cosmetics, fire retardant, fiberglass, fertilizer, insecticide, airplanes, medicine!
Zeolites
Water purification, catalysts, medicine
Uraninite
Nuclear power, x-rays
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
metallic
Quartz
glassy
Talc
Soapy, pearly
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
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
Selenite
Calcite
Fluorite Calcite with zincite
Diamond
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 Barth2007
Geology 114AUniversity of California, Santa BarbaraSome images herein borrowed from
websites have not been credited