Crystal Habit The term "crystal habit" is used to identify the shape, size and appearance of a crystal's unique growth characteristics, or "Crystal Forms". A particular mineral may exhibit several different habits, all of which are influenced by the following factors: • Crystal Twinning ( two individual crystals share some of the same crystal lattice points) • Growth Conditions (heat, pressure, and space) • Trace Impurities (present during crystal formation) 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 ►elongated crystals flattened like a knife blade: kyanite Dendritic ► arborescent, in slender divergent branches, somewhat plantlike--native metals, pyrolusite Radiating ► divergent: zeolite; tremolite; talc ► pyrolusite, tourmaline Drusy ►surface covered with a layer of small crystals--sugar like: calcite, quartz, sphalerite, pyrite 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 ►Fibreous tremolite ►chrysotile asbestos Globular and colloform ► radiating individuals forming small spherical groups ►examples include zeolites, quartz, malachite, goethite, pyrolusite, hematite Botryoidal ►bunch of grapes, example pyrolusite Reniform ►kidney like, examples hematite, malachite Foliated ►easily separable into plates or leaves: ►Micas are the ultimate example Micaceous ►similar to foliated but splits into very thin sheets: muscovite, biotite, chlorite Tabular or lamellar ►flat and plate-like: barite, dolomite Granular ►composed of many individual grains of similar size: olivine, garnet Prismatic or columnar ► elongated crystals with identical faces parallel to a common direction: tourmaline, hornblende, apatite Equant Crystal Habit ► Squashed, pinnacoids (terminating face) dominant over prisms Cubic Crystal Habit .