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Crystal Interfacial Angles

Crystal Interfacial Angles

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Crystal Interfacial Angles

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  1. Crystal Interfacial Angles • Even when the crystals are different sizes, angles between equivalent faces are the same • For different minerals, angles are different. 4 4 3 3 1 1 2 2 Quartz N. Lindsley-Griffin, 1999

  2. Habit Habit - distinctive shape of the way the mineral commonly (habitually) appears Concentric shells -- malachite N.Lindsley-Griffin, 1999

  3. Habit N. Lindsley-Griffin, 1998

  4. Crystal shape and Habit result from internal atomic structure N. Lindsley-Griffin, 1998

  5. Cleavage - tendency to break along planes of weak bonds N.Lindsley-Griffin, 1998

  6. Mica cleaves along planes of the weakest bonds N. Lindsley-Griffin, 1998

  7. Fracture describes how a mineral breaks on an irregular surface rather than along cleavage planes Types of fracture: Smooth Rough Splintery Conchoidal N. Lindsley-Griffin, 1998

  8. Hardness Hardness -- the resistance to being scratched Mohs scale measures relative hardness, the ability of one mineral to scratch another • Diamond 10 • Corundum 9 • Topaz 8 • Quartz 7 • Feldspar 6 Steel file (6.5) • Apatite 5 Glass (5.5- 6) • Fluorite 4 • Calcite 3 Copper penny (3.0) • Gypsum 2 Fingernail (2.5) • Talc 1 Mohs hardness scale: 1 = softest mineral; 10 = hardest © Houghton Mifflin 1998; Lindsley 2000

  9. The 10 minerals of Mohs relative hardness scale 4 Fluorite 3 Calcite 5 Apatite 1 Talc 2 Gypsum 10 Diamond 9 Corundum 6 Feldspar 7 Quartz 8 Topaz N. Lindsley-Griffin, 1999

  10. Luster Luster - the appearance of a mineral in reflected light Types of luster: Metallic Nonmetallic Pearly Vitreous Resinous Silky Dull Earthy Metallic luster of pyrite Earthy luster of limonite © Houghton Mifflin; N. Lindsley-Griffin, 1998.

  11. Metallic Luster is characteristic of ore minerals and others that contain metal cations. N. Lindsley-Griffin, 1998

  12. Resinous luster in sphalerite Pearly luster in talc N. Lindsley-Griffin, 1999