Minerals

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Minerals

• is a naturally-occurring, homogeneous solid with
  a definite, but generally not fixed, chemical
  composition and an ordered atomic arrangement. It
  is usually formed by inorganic processes.

• A mineral is an element or chemical compound
  that is normally crystalline and that has been
  formed as a result of geological processes"

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Let's look at the five parts of this definition
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"Naturally occurring"

• means that synthetic compounds not known to
  occur in nature cannot have a mineral name.
• However, it may occur anywhere, other planets,
  deep in the earth, as long as there exists a
  natural sample to describe.

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"Homogeneous solid"

• means that it must be chemically and physically
  homogeneous down to the basic repeat unit of the
  atoms.
• It will then have absolutely predictable
  physical properties (density, compressibility,
  index of refraction, etc.).
• This means that rocks such as granite or basalt
  are not minerals because they contain more than
  one compound.

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"Definite, but generally not fixed, composition"

• means that atoms, or groups of atoms must occur
  in specific ratios.
• For ionic crystals (i.e. most minerals) ratios
  of cations to anions will be constrained by
  charge balance, however, atoms of similar charge
  and ionic radius may substitute freely for one
  another hence definite, but not fixed.

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"Ordered atomic arrangement"

• means crystalline.
• Crystalline materials are three-dimensional
  periodic arrays of precise geometric arrangement
  of atoms.
• Glasses such as obsidian, which are disordered
  solids, liquids (e.g., water, mercury), and gases
  (e.g., air) are not minerals.

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"Inorganic processes"

• means that crystalline organic compounds formed
  by organisms are generally not considered
  minerals.
• However, carbonate shells are minerals because
  they are identical to compounds formed by purely
  inorganic processes.

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Six Crystal System

• Cubic
• Tetragonal
• Hexagonal
• Orthorhombic
• Monoclinic
• Triclinic

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Cubic
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Tetragonal
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Hexagonal
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Orthorhombic
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Monoclinic
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Triclinic
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A. Properties of minerals
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Color

• Obvious, but not always definitive.
• Sulfur is (almost) always yellow, and there are
  a few others, but not many minerals have a fixed
  color.
• Small amounts of impurities can drastically
  change a mineral's color.

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Luster

• The quantity and quality of light reflected from
  the surface.
• Metallic
• looks like a metal. Metallic minerals are
  commonly shiny and opaque
• Non-metallic
• doesn't look like a metal. There are many subtle
  differences in the non-metallic lusters, but most
  are relatively dull, and are often transparent to
  translucent on thin edges.

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Hardness

• is one measure of the strength of the structure
  of the mineral relative to the strength of its
  chemical bonds.

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Mohs Scale of Mineral Hardness

• was devised by the German mineralogist Frederich
  Mohs (1773-1839)
• who selected the ten minerals because they were
  common or readily available.
• The scale is not a linear scale.

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Hardness Mineral Associations and
Uses 1 Talc Talcum
powder. 2 Gypsum
Plaster of paris. Gypsum is formed when
seawater evaporates from the Earths surface.
3 Calcite Limestone and most shells
contain calcite. 4 Fluorite
Fluorine in fluorite prevents tooth decay.
5 Apatite When you are hungry you
have a big "appetite". 6
Orthoclase Orthoclase is a feldspar,
and in German, "feld" means"field". 7
Quartz 
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Hardness Mineral Associations and Uses
8 Topaz The November birthstone.
Emerald and aquamarine are varieties of
beryl with a hardness of 8.
9 Corundum Sapphire and ruby
are varieties of corundum.
Twice as hard as topaz. 10 Diamond
Used in jewelry and cutting tools. Four
times as hard as corundum.
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Hardness of some other items
2.5 Fingernail 2.53 Gold, Silver 3 Copper
penny 4-4.5 Platinum 4-5 Iron 5.5 Knife blade 6-7
Glass 6.5 Iron pyrite 7 Hardened steel file
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Field Hardness Kit
Hardness Item Comments 2.5
Fingernail We all have 10 of these to
wear out before taking off our shoes.
3.5 Penny Sometimes
all we have left. 4.5 Knife The hardness of
a blade can vary wildly depending on the
quality of your knife. Check yours before
going into the field so you'll
know. 5.5 Glass There's usually
a chunk of glass available. 7
Quartz A piece of quartz can be found
almost everywhere.
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Streak

• The color of the powdered mineral.
• The test is usually performed by scraping the
  mineral across a piece of unglazed porcelain.
• Streak can be definitive.

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Breakage pattern

• Fracture
• The mineral just breaks, leaving an uneven
  surface.
• Cleavage
• The mineral splits along closely spaces parallel
  planes, leaving a mirror surface which will flash
  at you if rotated in the light.
• Cleavage is controlled by the internal
  crystalline order of the mineral.
• A mineral can have 1, 2, 3, 4, or 6 planes of
  cleavage.

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Specific Gravity

• Defined as "the weight of a specific volume of a
  mineral divided by the weight of an equal volume
  of water (at 4C.)" Since water is always 1.0,
  it's the same number as density without any units
  (they cancel).
• This is almost impossible to measure in the
  field, but a rough approximation and be
  determined.

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Effervescence (the Fizz test )

• Minerals containing calcium carbonate (CaCO3)
  will generally react when exposed to weak acid
  (usually hydrochloric acid (HCl), but even
  vinegar will work).
• Carbon dioxide (CO2) is released and the mineral
  or rock literally "fizzes."

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