Chemical Formula

Na(Mg,Fe,Mn,Li,Al)3Al6Si6O18(BO3)3(OH)4

Hardness (Mohs)

7-7.5

Crystal System

Trigonal

Streak

White

Luster

Vitreous

Diaphaneity

Transparent to opaque

Color

Highly variable (can be black, brown, green, red, pink, blue, yellow, colorless, bi-color, tri-color)

Crystal Habit / Mode of Occurrence

Prismatic, often striated crystals with rounded triangular cross-section; massive, columnar, radiating, compact