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Mineral properties

Learn about the properties of minerals, including crystal habit, cleavage, color, specific gravity, hardness, and identification techniques such as optical mineralogy and X-ray crystallography.

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Mineral properties

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  1. Mineral properties Geology 101, Fall 2012

  2. The properties of minerals are determined by their chemical composition and crystal habit; there are over 7000 unique minerals

  3. Crystal habit • Crystal shapes are determined by local (nearest neighbor) intermolecular attractions

  4. Cleavage • Cleavage, on the other hand, relies on the alignment of weak areas held together by only intermolecular forces through the whole crystal

  5. Color (and luster) • Mineral color can be due to its intrinsic chemical composition (e.g., copper ores) or the crystal’s refractive properties or “impurities” such as a low concentration of metal ions not in the mineral’s chemical formula • Latter reason explains much of quartz’s color variability

  6. Specific gravity • SG is the ratio of the mineral’s density to water’s density; it can be thought of as a “unitless” density. • SG measures how efficiently packed the atoms are in a crystal, and gives some indication of composition (e.g., the lead in galena).

  7. Hardness • Hardness is an indication of molecule alignment in crystals (similar to cleavage) but also measures the strengths of the intermolecular forces

  8. Strength ≠ Hardness • Carbon nanowire is one of the strongest (tensile) materials known, but is no harder than graphite

  9. Sadly, minerals aren’t usually large enough to identify • So what techniques are available? • Optical mineralogy

  10. Optical mineralogy • Relies on the behavior of polarized light transmitted through a very thin cross-section of a rock sample

  11. X-ray crystallography • Basic premise: shoot X-rays at a crystal, look at the shadow pattern of atoms, determine structure and, eventually, identity

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