Minerals

A mineral is

• a naturally occurring,
• inorganic solid
• with crystalline form,
• and specific chemical composition.

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
• optical properties such as double refraction.