Physical properties
Habit: massive, granular, prismatic.
Color: white, gray, brown, brownish gray, or reddish
white.
Diaphaneity: transparent to opaque.
Luster: vitreous, greasy.
Streak: white.
Cleavage: (1010) poor.
Twinning: {100}, {112}, and {335}.
Fracture: Subconchoidal.
Occurrence: Silica-poor igneous rocks.
