Minerals

Properties of Minerals

Crystal Form

• Each mineral exhibits its own orderly internal arrangement of atoms
• Given enough space, each mineral will externally express this orderly arrangement developing well formed crystals

Luster

• The appearance or quality of light reflected from the surface of a mineral
• Minerals can have metallic luster giving a metallic shiny appearance
• Minerals can have non-metallic luster
  Non-metallic luster minerals are described as...
  • vitreous = glass-like in appearance
  • pearly
  • silky
  • resinous
  • dull = earthy
• A third category of luster, sub-metallic, appear somewhat metallic in luster

Streak

• The color of a mineral in powdered form is its streak
• The streak is obtained by striking a mineral across an unglazed porcelain plate
• The streak color of a mineral is usually a more reliable identification property than the color of the mineral because it does not vary from sample to sample
  • Metallic luster minerals have a dark, dense streak
  • Non-metallic luster minerals have thinner, lighter streaks

Color

• An unreliable diagnostic property because slight impurities cause vast color differences

Hardness

• A measure of the resistance of a mineral to scratching or abrasion is known as its hardness
• Hardness is very useful in mineral identification
  The Mohs Hardness Scale is used by geologists for mineral identification
  • 10 minerals of known hardness are arranged from hardest(10) to softest(1)
  • By scratching an unknown mineral with a mineral of known hardness, the unknown mineral's hardness can be determined
    • if 2 minerals are of the same hardness, they will not scratch each other
    • a harder mineral will scratch a softer one
  • Other tools may be useful in hardness tests
    • a fingernail has a 2.5 hardness
    • a copper penny has a 3.5 hardness
    • a piece of glass has a 5.5 hardness

Cleavage

• The tendancy of a mineral to break along planes of weaker bonds is cleavage
• Smooth surfaces are produced in cleavage
• Cleavage occurs when minerals break evenly and is described by the number of cleavage planes

Fracture

Minerals that do not exhibit cleavage, fracture

• Conchoidal fracture - break into smooth curved surfaces
• Splinters or fibers
• Irregular fracture

Specific Gravity

• Specific gravity compares the weight of a mineral to the weight of an equal volume of water

Other Properties

• texture - greasy, soapy
• malleability
• taste (not recommended)
• magnetic
• smell
• optical properties
• effervescence
• elasticity

Test your knowledge with this ten question quiz: http://www.cobweb.net/~bug2/mineral.htm