3 Al 2 SiO 6 Color Bright to pale green, light to dark blue, blue-green, yellow, pink, purple, red, brown, colorless, white, and gray. Some specimens are a lighter color on one end of the crystal than on the other, and some unusual multicolored blue and white or green and white specimens also exist.
Crystals are prismatic hexagons , and usually occur individually.
Crystals may be enormous. Also occurs in short, stubby crystals, and occasionally in tabular crystals and plates . Crystals are usually not terminated , and their bases are either flat or damaged. Even when terminated, they are rarely fully terminated like a bipyramidal hexagon . Also occurs in columnar aggregates and massive .