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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
Habit

Shape and appearance of mineral growth

acicular
Acicular
  • slender, needle-like crystals:tourmaline, hornblende, arsenopyrite, rutile, apatite, sillimanite
capillary and filiform
Capillaryandfiliform
  • hair-like or thread-like: native Au, Ag, Cu
      • Very thin
bladed
Bladed
  • elongated crystals flattened like a knife blade: kyanite
dendritic
Dendritic
  • arborescent, in slender divergent branches, somewhat plantlike--native metals, pyrolusite
radiating
Radiating
  • divergent: zeolite; tremolite; talc
  • pyrolusite, tourmaline
drusy
Drusy
  • surface covered with a layer of small crystals--sugar like: calcite, quartz, sphalerite, pyrite
dodecahedral
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.
fibrous
Fibrous
  • aspect ratio 10:1
  • chrysotile asbestos
globular and colloform
Globular and colloform
  • radiating individuals forming small spherical groups
  • examples include zeolites, quartz, malachite, goethite, pyrolusite, hematite
botryoidal
Botryoidal
  • bunch of grapes, example pyrolusite
reniform
Reniform
  • kidney like, examples hematite, malachite
foliated
Foliated
  • easily separable into plates or leaves:
      • Micas are the ultimate example
micaceous
Micaceous
  • similar to foliated but splits into very thin sheets: muscovite, biotite, chlorite
tabular or lamellar
Tabular or lamellar
  • flat and plate-like: barite, dolomite
granular
Granular
  • composed of many individual grains of similar size: olivine, garnet
prismatic or columnar
Prismatic or columnar
  • elongated crystals with identical faces parallel to a common direction: tourmaline, hornblende, apatite
equant crystal habit
Equant Crystal Habit
  • Squashed, pinnacoids (terminating face) dominant over prisms
types of crystals
Types of crystals
  • Euhedral
  • Subhedral
  • Anhedral
  • Amorphous
twinning
Twinning
  • Crystals that are related to one another by some geometric relation.
how does it happen
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.
how do we recognize them
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
polysynthetic multiple
Polysynthetic (multiple)
  • e.g. Plagioclase
parting
Parting
  • Occurs when a mineral breaks along a twin plane