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Content. Crystal Form Luster Color Streak Hardness Cleavage Fracture Specific Gravity. Physical properties of minerals. Primary diagnostic properties Determined by observation or performing a simple test Several physical properties are used to identify hand samples of minerals.

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  1. Content • Crystal Form • Luster • Color • Streak • Hardness • Cleavage • Fracture • Specific Gravity

  2. Physical properties of minerals • Primary diagnostic properties • Determined by observation or performing a simple test • Several physical properties are used to identify hand samples of minerals

  3. Physical properties of minerals • Crystal form • External expression of a mineral’s internal structure • Often interrupted due to competition for space and rapid loss of heat

  4. Crystal System

  5. Cubic crystals of pyrite

  6. A garnet crystal

  7. Physical properties of minerals • Luster • Appearance of a mineral in reflected light • Two basic categories • Metallic • Nonmetallic • Other descriptive terms include vitreous, silky, earthy, waxy or others ..

  8. Pyrite displays metallic luster

  9. Kaolinite displays earthy luster

  10. Quartz displays vitreous luster

  11. Satin spar displays silky luster

  12. Jade displays Waxy luster

  13. Physical properties of minerals • Color • Generally unreliable for mineral identification • Often highly variable due to slight changes in mineral chemistry • Exotic colorations of certain minerals produce gemstones

  14. Quartz (SiO2) exhibits a variety of colors

  15. Trace ions give glass its distinctive colors

  16. Physical properties of minerals • Streak • Color of a mineral in its powdered form Small amounts of an impurity that strongly absorbs a particular wavelength can radically change the wavelengths of light that are reflected by the specimen, and thus change the apparent color. However, when the specimen is dragged to produce a streak, it is broken into randomly oriented microscopic crystals, and small impurities do not greatly affect the absorption of light.

  17. Hematite Streak is obtained on an unglazed porcelain plate

  18. Physical properties of minerals • Hardness • Resistance of a mineral to abrasion or scratching • All minerals are compared to a standard scale called the Mohs scale of hardness

  19. Mohs scale of hardness Mohs scale relates the hardness of minerals with some common objects, such as fingernails, copper pennies, a steel knife blade, and glass.

  20. Physical properties of minerals • Cleavage • Tendency to break along planes of weak bonding • Produces flat, shiny surfaces • Described by resulting geometric shapes • Number of planes • Angles between adjacent planes

  21. Common cleavage directions

  22. Fluorite, halite, and calcite all exhibit perfect cleavage

  23. Schematic diagram of the crystalline structure of sodium chloride, more commonly known as table salt. The actual ions are very closely packed.

  24. Physical properties of minerals • Fracture • Absence of cleavage when a mineral is broken

  25. Physical properties of minerals • Specific Gravity • Weight of a mineral / weight of an equal volume of water • Average value = 2.7

  26. Physical properties of minerals • Other properties • Magnetism • Reaction to hydrochloric acid • Malleability • Double refraction • Taste • Smell • Elasticity

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