Minerals

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Minerals

• Chapter 5

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Minerals

• naturally occurring non living solid that has a
  definite composition and structure
• 4000 different minerals
• naturally occurring- not made by man
• inorganic- not alive, never was alive, didnt
  come from living materials
• definite structure- atoms arranged in repeating
  patterns
• definite composition- specific chemical formula
• barite (BaSO4)
• talc Mg3Si4O10(OH)2

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2 Main Composition Groups

• silicates
• (largest group) -Si -O
• non-silicates
• carbonates -CO3
• oxides -O
• sulfides -S
• halides -Cl or -F
• sulfates -SO4
• native elements not combined with any other
  atom

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Crystal Systems

• Atoms arranged in repeating patterns
• Not all samples show flat sides and sharp edges,
  it depends on where and conditions of the sample
  when it formed
• Constrictive environment creates small crystals,
  or masses of interlocking crystals
• Not restrictive environment allows crystals to
  grow large

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How Minerals Form

• Cooling of hot magma (hot melted rock)
• Liquids containing the mineral evaporates,
  leaving the mineral

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6 Major Crystal Systems

• Cubic- (halite)
• Orthorhombic- (sulfur)
• Tetragonal
• Monoclinic- (gypsum)
• Hexagonal- (quartz)
• Triclinic
• why 6?
• Lengths of the axis and the angles at which the
  axis intersect determines the crystal system

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Physical Properties

• Unique properties or descriptions that help to
  identify minerals
• Hardness
• Luster
• Color
• Streak
• Cleavage vs. Fracture
• Specific Gravity
• Special properties

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Hardness

• How easily a mineral can be scratched

• Mohs Hardness Scale-------------------Tools
• talc
• gypsum 2.5 fingernail
• calcite 3.5 copper penny
• fluorite 4.5 iron nail
• apatite 5.5 glass plate
• feldspar 6.5 steel file
• quartz 7.0 streak plate
• topaz
• corundum tools we will use in lab.
• diamond to determine a minerals hardness

• A higher number mineral will scratch a lower
  number mineral

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Luster

• How light is reflected from a mineral
• metallicshines like a metal
• nonmetallicdoes not shine like a metal
• can be dull, pearly, glassy, silky, brilliant

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Color

• Look at mineral to recognize the color
• Usually a bad way to identify minerals, because
  most minerals can be different colors
• sulfur, olivine, orthoclase, malechite, copper

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Streak

• the color of the mineral in powder form
• Use streak plate for minerals with hardness less
  than 7!

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Cleavage

• Tendency for a mineral to break along smooth flat
  surfaces
• Why?
• Orderly arrangement of atoms causes a weakness
  where bonds arent as strong. Relates chemical
  makeup and chemical structure
• Cleavage is expressed in number of directions of
  cleavage the angles at which they intersect

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Directions of Cleavage

• 1 directionsheets of paper
• 2 directionsa box with open top and bottom
• 3 directionsa brick
• Can have more than three, but it is difficult to
  see except in a fluorite octahedral

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Angles of Cleavage

• Angles between the directions of cleavage are
  either 90o or NOT 90o
• Also described as perfect (easy to see) or poor
  (hard to see)

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Fracture

• curved, broken of jagged edges without flat
  surfaces
• special type of fractureconchoidal fracture
  looks like a shell with curved pattern seen in
  quartz

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Specific Gravity

• Mass per unit of volume compared to H2O (density
  of mineral compared to the density of water)
• It is heavy for its size??

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Special Properties

• Optical properties- transparent or translucent
• double refraction of calcite 
• Reaction to acid- members of the carbonate group
  fizz when put into acidCO2 gas bubbles
• ex. calcite, malachite 
• Magnetism- some minerals are magnetic, others are
  attracted to a magnet
• ex. magnetite
• Taste
• ex. halite is salty

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Special Properties

• Iridescence- rainbow colors like soap bubbles
• ex. Labradorite
• Chatoyancy- cats eye effect
• Asterism- six sided star appears in the mineral
• Phosphorescence or fluorescence- how minerals
  behave in ultraviolet light. Some change colors,
  some glow in the dark