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Identifying Minerals. Crystal Form. Some minerals can form distinctive crystalline shapes that make them very recognizable. Ex: Halite (cubic), Quartz (Six-sided and pointed). Not all minerals will form perfect crystals and so identification based only on crystal form is rare. Luster.

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crystal form
Crystal Form
  • Some minerals can form distinctive crystalline shapes that make them very recognizable. Ex: Halite (cubic), Quartz (Six-sided and pointed).
  • Not all minerals will form perfect crystals and so identification based only on crystal form is rare.
luster
Luster
  • The way that a mineral reflects light from its surface is called luster.
  • Two types: Metallic and Non-metallic luster.
  • Metallic: silver, gold, copper
  • Non-Metallic: They do not shine like metals. Instead, they could be described as dull, pearly, waxy.
  • Rather subjective and so luster should be used in conjunction with another process.
hardness
Hardness
  • A very useful and reliable test for identifying minerals.
  • Hardness is a measure of how easily a mineral can be scratched.
  • The German geologist Friedrich Mohs developed a scale by which an unknown mineral’s hardness can be compared to the known hardness of ten minerals.
cleavage fracture
Cleavage & Fracture
  • The arrangement of atoms within a crystal will determine how a mineral will break. Minerals break along planes where atomic bonding is weak.
  • A mineral that splits relatively easily and evenly along one or more flat planes is said to have cleavage. (ex: Mica and Halite)
  • Minerals that break with rough or jagged edges are said to have fracture. Ex: Flint (conchoidal fracture)
streak
Streak
  • Streak is the colour of the mineral when it is broken up and powdered. This can usually be seen by running a mineral across an unglazed porcelain plate.
  • Non-metallic minerals – usually white
  • Metallic minerals – varies (most useful for metallic minerals)
  • Can you use streak to identify all minerals? Why or why not?
colour
Colour
  • A very noticeable feature of a mineral and yet one of the least useful.
  • Colour is often the result of trace elements within the mineral.
  • Ex: Quartz (Amethyst, Rose Quartz, Red Jasper, Citrine)
density and specific gravity
Density and Specific Gravity
  • Density = mass/volume
  • Density does not depend on the size and shape of a mineral. It only depends on the internal atomic structure. For this reason, it is a useful identification tool.
  • If the sample is too small, it is difficult to determine the density by conventional means. Therefore, geologists typically measure density by determining a materials specific gravity.
  • Specific gravity – ratio of the mass of a substance to the mass of an equal volume of water at 4 degrees Celsius.
texture
Texture
  • How does a mineral feel to the touch?
    • Similar to luster, this is a subjective measurement.
    • Ex: Talc is greasy and Fluorite is smooth.
special properties
Special Properties
  • Double Refraction – Iceland Spar (Calcite)
  • Effervescence – Calcite will fizz when exposed to an acid (release of carbon dioxide)
  • Magnetism – Magnetite (iron containing minerals)
  • Iridescence – Labradorite (caused by the bending of light rays)
  • Fluorescence – Fluorite, Calcite (glows in the dark when exposed to UV light)