Mineral Identification

Each layer of the Earth has a different density

Earth density

Thickness of each layer:

  • Crust - 5-30 miles
  • Mantle - 1800 miles
  • Core - 2000 miles

Matter of the Lithosphere

Lithosphere: outer portion of the crust

  • 2000 Minerals
  • 88 Elements

Rock formers: 9 abundant elements in the litosphere

Common elements that make up the minerals of the crust, in decreasing abundance:

  1. Oxygen
  2. Silicon
  3. Aluminum
  4. Iron
  5. Calcium
  6. Sodium
  7. Potassium
  8. Magnesium
  9. Titanium

Organic: Once living; ex: coral, mollusk, shells

Inorganic: Never living

Minerals..

  • are inorganic
  • formed in nature
  • solids
  • have a definite internal atomic pattern
  • have a specific chemical composition (compound)

We can observe the internal atomic pattern by use of X-ray defraction.

If the arrangement of the molecules is large enough to be recognized by the eye, we call it a Crystal.

Large crystals are uncommon because when crystals start to form they interfere with each other. Instead of growing into large recognizable crystals, the crystals grow together -- the mineral is said to be massive.

Mineralogist: a scientist who studies minerals.

Groups of Minerals

  1. Silicates

    Si + O -- largest group; 87% of the crust

  2. Carbonates

    C + O

    • Ca + C + O2 => CaCO2
    • Mg + C + O2 => MgCO2
    • Fe + C + O2 => FeCO2

    To test for a carbonate, place a drop of HCl (hydrochloric acid) on the sample. If it fizzes, it's a carbonate.

  3. Oxides

    O2 + some other element, e.g. Fe2O3

Tetrahedron structure: basic unit of all silicates

Silica is SiO4. The atoms are arranged with Si in the center:

Silica

Crystal faces: the flat surfaces which join at well defined angles.

The angle between crystal faces is always the same, regardless of size.

Identification of Minerals

  1. Luster: the wasy that it reflects light

    1. Metallic: looks like a metal
    2. Non-metallic: does not reflect light like a metal

    Non-metallic luster terms:

    • Adamantine - sparkles like a diamond
    • Vitreous - like a broken edge of glass
    • Greasy
    • Pearly
    • Silky
    • Waxy
    • Dull - lacks luster; scatters light
    • .. other terms can also be used

  2. Streak: the color of the powdered mineral

    Rub the mineral on a porcelain plate. The color that comes off the mineral is called the streak color.

    3. Streak plate

  3. Hardness: resistance to being scratched

    Materials needed

    Mohs Scale of Hardness

    Mohs Scale Field Test
    1. Talc Soft, feels greasy Talc
    2. Gypsum Scratched by fingernail Gypsum
    3. Calcite Scratched by a penny Calcite
    4. Fluorite Easily scratched by a knife blade Fluorite
    5. Apatite Scratched by a knife blade with difficulty Apatite
    6. Feldspar Scratched by glass Feldspar
    7. Quartz Will scratch glass Quartz
    8. Topaz Scratches quartz Topaz
    9. Corundum Scratches topaz Corundum
    10. Diamond Scratches corundum Diamond

  4. Shape: external appearance

    1. Amorphous: without a definiate shape, massive
      Graphite
    2. Crystal: definite geometric pattern; count the number of crystal faces
      Quartz crystal

    Some terms that can be used for minerals that have a definite shape:

    • Prismatic
    • Micaceous
      Muscovite
    • Acicular
    • Pisolitic
    • Tabular
    • Oolitic
    • Fibrous
      Asbestos

  5. Breakage

    1. Cleavage: breaks along smooth plane, surfaces that are parallel to the opposite surface: 1-, 2-, or 3- direction cleavage.
      Galena
    2. Fracture: the broken surfaces are not smooth planes; breakage is irregular.
      Olivine
      Examples: rough, ragged, uneven
      Conchoidal Arrowhead
      Conchoidal

  6. Specific gravity

    The ratio of the weight of a mineral to the weight of an equal volume of water.

    Specific gravity tells you how many times as heave as water the mineral is

    Specific Gravity = (weight in air) / (loss of weight in water)

  7. Color

    The outward color, NOT streak color

    Color is usually not an important quality

    Some minerals vary in color; e.g. quartz can be: clear, white, pink, purple, smokey.

    Many minerals have the same colors or similar colors; e.g. fluorite and quartz can both be purple.

    Quartz Amethyst

  8. Special characteristics

    • Taste
      Halite
      Halite (table salt)
    • Shape
      Recangular, cubic, pyramidal, etc
    • Double refraction
      Double refraction
    • Fluorescence
    • Radioactive

  9. Transparency

    The ease with which light will pass through it.

    • Transparent: most light passes through
    • Translucent: some light passes through
    • Opaque: all the light is absorbed or reflected