Minerals

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Minerals
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• Rocks are what Earth is made of. Minerals are
  what rocks are made of.

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• Minerals are naturally occurring, inorganic
  solids with an orderly crystalline structure and
  a definite chemical composition.

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• Naturally occurring means that it is formed by
  natural geologic processes.
• Solid, means it is solid within the temperature
  ranges that are normal or Earths surface. Water
  is not a mineral even though it occurs naturally.
  But, ice is.
• Orderly crystalline structure. This means that
  the atoms line up in a repetitive pattern.

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• Definite chemical composition means that most
  minerals are compounds of more than one element.
  Only a few (such as gold) consist of only a
  single element
• Generally considered inorganic, sugar is a
  crystalline solid but it comes from plants. Salt
  is inorganic.

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• How do minerals form?
• There are four major processes -

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• Crystallization from magma - as magma cools,
  elements combine to form minerals. Minerals form
  in a predictable order as magma cools.
• Precipitation - many minerals are dissolved in
  water on Earth. Changes in water temperature may
  cause dissolved material to precipitate out or
  minerals may combine with each other.

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• Changes in pressure and temperature - in a rock
  that is already solid, changes in pressure and
  temperature may cause new minerals to form from
  old ones. The atoms are rearranged to form more
  compact minerals.

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• Formation from hydrothermal solutions - hot
  mixtures of water and dissolved substances may
  come into contact with existing minerals. This
  can cause new minerals to form.

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Mineral Groups
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• Silicates - The silicates are the largest, the
  most interesting and the most complicated class
  of minerals by far.
• Approximately 30 of all minerals are silicates
  and some geologists estimate that 90 of the
  Earth's crust is made up of silicates.
• With oxygen and silicon the two most abundant
  elements in the earth's crust silicates abundance
  is no real surprise.

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• The basic chemical unit of silicates is the
  (SiO4) tetrahedron shaped anionic group with a
  negative four charge (-4). The central silicon
  ion has a charge of positive four while each
  oxygen has a charge of negative two (-2) and thus
  each silicon-oxygen bond is equal to one half
  (1/2) the total bond energy of oxygen.

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• This condition leaves the oxygens with the option
  of bonding to another silicon ion and therefore
  linking one (SiO4) tetrahedron to another and
  another, etc
• This condition leaves the oxygens with the option
  of bonding to another silicon ion and therefore
  linking one (SiO4) tetrahedron to another and
  another, etc..

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• The complicated structures that these silicate
  tetrahedrons form is truly amazing. They can form
  as single units, (like quartz), double units,
  chains, sheets, rings and framework structures.

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• The different ways that the silicate tetrahedrons
  combine is what makes the Silicate Class the
  largest, the most interesting and the most
  complicated class of minerals.
• The place of formation (temperature and pressure)
  and the chemical composition of the magma
  determine which silicate mineral will form.
• Quartz crystals form at about 700º C
• Olivine crystallizes at about 1200º C
• Geologists can provide scientists clues about the
  conditions in which the minerals formed.

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• Carbonates are the second most common mineral
  group
• They contain the element carbon, oxygen and one
  or more other metallic elements.
• Calcite is the most common carbonate mineral.
• Limestone and marble are composed of carbonate
  minerals

limestone
Marble
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• Oxides are minerals
• that contain oxygen
• and one or more other
• elements which are
• usually metals.
• Ti2O us titanium oxide
• Al2O3 is corundum (ruby and sapphire)
• Fe2O3 is hematite

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• Sulfates and Sulfides are minerals that contain
  the element sulfur.
• PbS is galena
• ZnS is sphalerite
• FeS2 is pyrite

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• Halides are minerals that contain a halogen ion
  plus one or more other elements
• Halogens are elements from Group 7A of the
  periodic table.
• NaCl is a halide, table salt
• CaF2 is fluorite

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• Native elements are minerals that exist in
  relatively pure form.
• This can include gold (Au), silver (Ag), copper
  (Cu), sulfur (S) and carbon (C).
• Native forms of carbon are diamond and graphite

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Properties Of Minerals

• Color - this is often not a good way to identify
  a mineral because trace elements can give the
  same mineral different colors.
• Streak - this is the color of a mineral in its
  powdered form. The test is made by rubbing a
  mineral across a streak plate

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• Luster - how is light reflected from the surface
  of a mineral?
• Metallic, Sub-metallic or Non-metallic
• Adamantine the brightest, usually occurs in
  minerals with a high refractive index (e.g.
  diamond)
• Resinous (e.g. sulfur)
• Vitreous glass-like
• Pearly slightly iridescent
• Silky usually in fibrous minerals
• Waxy (e.g. chalcedony)
• Earthy very dull luster, usually in minerals
  with a rough surface

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• Crystal form is the visible expression of a
  minerals internal arrangement of atoms.
• Hardness - is a measure of the resistance of a
  mineral to being scratched. Geologists use a
  standard measure of hardness called the Mohs
  scale. The Mohs scale consists of 10 minerals
  arranged from 10 (hardest) to 1 (softest)

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• Cleavage is the tendency of a mineral to cleave
  or break along flat even surfaces. Micas cleave
  in horizontal plates. Cleavage shows where a
  minerals internal bonds are strong and weak.
• Fracture is the way a mineral breaks when struck
  with a hammer. Minerals that do not cleave,
  fracture.

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• Density is a property of all matter that is the
  ratio of an objects mass to its volume. The
  units are mass/volume. In SI, density is
  measured in g/cm3.
• Distinctive properties - some minerals have
  distinctive properties. Calcite exhibits double
  refraction. Sulfur compounds smell like rotten
  eggs. Carbonate minerals will fizz when they
  come into contact with HCl.