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Habit

Habit . Shape and appearance of mineral growth. Acicular. slender, needle - like crystals: tourmaline, hornblende, arsenopyrite, rutile, apatite, sillimanite. Capillary and filiform. hair-like or thread-like: native Au, Ag, Cu Very thin. Bladed.

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Habit

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  1. Habit Shape and appearance of mineral growth

  2. Acicular • slender, needle-like crystals:tourmaline, hornblende, arsenopyrite, rutile, apatite, sillimanite

  3. Capillaryandfiliform • hair-like or thread-like: native Au, Ag, Cu • Very thin

  4. Bladed • elongated crystals flattened like a knife blade: kyanite

  5. Dendritic • arborescent, in slender divergent branches, somewhat plantlike--native metals, pyrolusite

  6. Radiating • divergent: zeolite; tremolite; talc • pyrolusite, tourmaline

  7. Drusy • surface covered with a layer of small crystals--sugar like: calcite, quartz, sphalerite, pyrite

  8. Dodecahedral • Also commonly seen in Garnets, as in this lab • 12 sided crystal growth. • NOTE: Rhombohedral, Cubic, etc. are also geometric habits, i.e. how the crystal grows.

  9. Fibrous • aspect ratio 10:1 • chrysotile asbestos

  10. Globular and colloform • radiating individuals forming small spherical groups • examples include zeolites, quartz, malachite, goethite, pyrolusite, hematite

  11. Botryoidal • bunch of grapes, example pyrolusite

  12. Reniform • kidney like, examples hematite, malachite

  13. Foliated • easily separable into plates or leaves: • Micas are the ultimate example

  14. Micaceous • similar to foliated but splits into very thin sheets: muscovite, biotite, chlorite

  15. Tabular or lamellar • flat and plate-like: barite, dolomite

  16. Granular • composed of many individual grains of similar size: olivine, garnet

  17. Prismatic or columnar • elongated crystals with identical faces parallel to a common direction: tourmaline, hornblende, apatite

  18. Equant Crystal Habit • Squashed, pinnacoids (terminating face) dominant over prisms

  19. Types of crystals • Euhedral • Subhedral • Anhedral • Amorphous

  20. Crystal Growth is not always perfect

  21. Twinning • Crystals that are related to one another by some geometric relation.

  22. How does it happen? • Errors occur during the crystallization of a mineral • This error can be caused by random flaws in nature. • During growth phases • High temperature phase to a low temperature phase • Siamese twins • never random and follows certain defined rules called twin laws.

  23. How do we recognize them? • recognized by penetration angles or notches in the crystal • Contact • Planes that forms the boundary between the twins • Penetration • Two crystals grew into/out of each other • Simple or complex • 2 or more than 2

  24. Simple

  25. Penetrative

  26. Polysynthetic (multiple) • e.g. Plagioclase

  27. “Cyclic”

  28. Parting • Occurs when a mineral breaks along a twin plane

  29. Hopper Crystals

  30. Dendrites

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