Hornblende

Color: Is almost always black to dark green.

Streak: Brown to gray.

Luster: vitreous to dull

Habit: Short stocky prismatic crystals as well as long thin crystal forms. Crystals can have a hexagonal cross-section although rarely symmetrical. The typical termination, if seen, appears as the two faces of a dome but is actually two of the four faces of a prism. Also found granular, massive and occassionally acicular aggregates.

Hardness: 5 - 6

Specific gravity: 2.9 - 3.4

Cleavage: 2; imperfect in two directions at 56 and 124 degrees.

Tenacity: Brittle

Twinning: Common on {100}, contact, simple, repeated; on {001}, lamellar

Crystal system: Monoclinic

Crystal class: 2/m

Unit cell: a = 9.70 Å, b = 8.84 Å, c = 5.27 Å, b = 106.97°

Synonyms/varieties: Fassite (Fe3+, Al-rich var.), ferrohedenbergite, jeffersonite (Mn, Zn-rich var.), violan (Fe=Mg var.), asteroite (Fe-rich var.)