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Identifying Minerals Section 5.2
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Objectives Describe seven physical properties that help distinguish one mineral from another. List 5 special properties that may help identify certain minerals
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Physical properties of minerals are a result of the chemical composition and crystalline structure
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Talc is highly variable, yet Sulfur is almost always yellowish.
Color: Can be very characteristic for a few minerals, but is not important for others Talc is highly variable, yet Sulfur is almost always yellowish. Talc Sulfur Talc
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Luster: the way light is reflected either Metallic or Non-metallic
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Non-metallics are further described as:
dull (earthy) waxy glassy (transparent) pearly (translucent)
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Hematite has a very red streak
Streak: the color of the powdered mineral Hematite has a very red streak
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Cleavage and Fracture how a mineral splits or how a mineral breaks
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The Six Crystal Systems
Isometric Orthorhombic Tetragonal Hexagonal Monoclinic Triclinic
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Isometric System Three axes of equal length intersect at 90 degree angles. Examples: Galena, halite, and pyrite.
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Pyrite and Halite
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Tetragonal System Three axes intersect at 90 degree angles.
Horizontal axes of equal length. Vertical axis can be longer or shorter than the other two. Examples: Cassiterite, chalcopyrite, and zircon.
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Cassiterite and Zircon
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Orthorhombic System Three axes of different lengths intersect at 90 degrees. Examples: Olivine, topaz, and staurolite.
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Olivine (Peridot) and Topaz
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Hexagonal System Three horizontal axes of the same length intersect at 60 degree angles The vertical axis may be longer or shorter than the horizontal axes. Examples: Calcite, hematite, and quartz.
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Calcite and Quartz (Amathyst)
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Monoclinic System Three axes of different lengths, two intersect at 90 degree angles. The third axis is oblique (inclined) to the others. Examples: Micas, gypsum, microcline (orthoclase)
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Gypsum and Orthoclase (Amazonstone)
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Triclinic System Three axes of unequal length that are oblique (inclined) to each other. No 90 degree angles. Examples: Plagioclase feldspars, turquoise, and axinite.
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Moh’s Hardness Scale
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We use a scale from 1 to 10 called MOH’S SCALE OF HARDNESS.
Talc is a 1 and diamond is a 10. Most minerals fall between The field scale can be very helpful:
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Field Scale of Hardness
Finger Nail 2.5 Penny Nail or Knife to 5.5 Glass to 6.0
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Specific Gravity (heft):
Density = Mass/Volume SG = Density of Sub./Density of H2O Dry weight of Mineral SG = Dry weight - weight in water
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Example low and high Specific Gravity
Galena (high) Graphite (low)
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Unique Characteristics of a few minerals
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Magnetism: Some minerals are attracted to a magnet. Magnetite
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Fluorescence: Minerals which will glow under an ultraviolet (black) light. Opal Minerals that continue to glow after the ultraviolet light is cut off are called phosphorescent.
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Chatoyancy and Asterism
Chatoyancy: Silky appearance due to large numbers of parallel mineral fibers. Asterism: Six-sided star shape when the mineral reflects light.
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Radioactivity: Some radioactive minerals will emit charged particles that are detected by a geiger counter. Uranitite
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Malleability: Some minerals are bendable Some minerals are brittle
Copper Garnet
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Feel: Some minerals feel greasy or soapy (unctuous) Graphite
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Solubility: Some minerals are soluble (will dissolve) in water Halite
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Iceland Spar (Calcite)
Double Refraction: Optical properties reveal a double image Iceland Spar (Calcite)
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Taste: Some minerals taste salty. Halite
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React with acids: Carbonates react with hydrochloric acid and give off CO2 gas Calcite
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