Some sugilite has been cut into gemstones, but these are very rare. The primary structural unit of sugilite is a most unusual double ring , with a formula of Si 12 O 30 . The structure is analogous to the dual wheels of a tractor trailer and is shared by other members of the Milarite - Osumilite Group . Color is purple, brown to yellow, pale pink and even black. Luster is vitreous to dull or waxy.
Crystals are translucent to opaque.
Crystal Habits include rare striated prismatic crystals, but specimens are usually massive. Cleavage is poor in one direction. Fracture is subconchoidal. Streak is brown. Associated Minerals include pectolite , poudretteite and polylithionite .