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Identifying Minerals

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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Identifying Minerals

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  1. Identifying Minerals

  2. 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.

  3. 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.

  4. 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.

  5. 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)

  6. Cleavage & Fracture

  7. 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?

  8. 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)

  9. 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.

  10. 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.

  11. 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)

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