Translucent to opaque. Color banded or mottled appearance common. Not wholly crystalline. Vitreous Typically elongated prismatic crystals with striated faces and triangular cross section. Common variety shiny black.
Crystals often occur in parallel or radiating groups.
Color and hardness aid identification transparent to opaque. Colorless, white, pink, blue, light green, emerald green Vitreous Commonly pale green, and in 6-sided prisms with flat terminations. Harder than quartz. Striations on crystal faces. Distinct glassy prismatic crystals with perfect basal cleavage exhibiting diamond-shaped cross section.