Minerals

A mineral has these characteristics:

The physical properties of minerals allow identification of many minerals using simple techniques:

Luster
 
  • The appearance of the light reflected from the mineral's surface.
  • Metallic - Strong reflections produced by opaque substances.
  • Non-metallic
    • Adamantine - brilliant luster of diamond.
    • Dull -
    • Earthy - like dried mud
    • Greasy - appearance of being coated with an oily substance.
    • Pearly - white iridescence of materials such as pearls.
    • Silky - sheen of fibrous materials such as silk.
    • Vitreous - bright, as in glass.
Color
Color can be misleading since small impurities can greatly change a mineral's color.
Streak
 
  • The color of the powdered mineral is more reliable than the mineral's color.
  • Rubbing a mineral on an unglazed porcelain plate yields a diagnostic streak of powdered mineral.
Cleavage
 
  • Some minerals will break along lines of weakness according to the chemical bonds that make up the mineral.
  • The flat surfaces produced also vary in smoothness.
  • The ease with which a mineral can be cleaved varies.
  • Some minerals have such strong bonding that the fracture rather than cleave.
Fracture
This is the way some minerals break along irregular surfaces.
Specific Gravity
The number ratio of the weight of a specific volume of mineral compared to an equal volume of water.
Crystal Form
The external form that a mineral has reflecting the orderly internal arrangement of its atoms. Do you notice a regular, repeating pattern to the crystals of the mineral?
Hardness
1 talc 5.2 knife blade
2 gypsum 5.8 window glass
2.5 fingernail 6 orthoclase
3 calcite 7 quartz
3.5 copper penny 8 topaz
4 fluorite 9 corundum
5 apatite 10 diamond
 
  • The strength of a mineral's chemical bonds determines its resistance to scratches or abrasion.
  • A standard scale of mineral hardness was devised in 1822 by Freidrich Mohs.
  • The Mohs scale uses common minerals and objects as benchmarks.
  • These benchmarks do not follow a linear progression of increasing hardness.

Other Properties include
 
  • reaction to weak hydrochloric acid (HCl)
  • magnetism
  • taste - not recommended!
  • feel
  • elasticity
  • radioactivity
  • optical properties such as double refraction or fluorescence.