Habit: prismatic according to b, striated, columnar. Color: gray, apple green, brown, blue,
or rose red. Diaphaneity: transparent to translucent. Luster: vitreous (i.e., glassy),
resinous, pearly. Streak: white. Cleavage: [001] perfect, [100] imperfect. Fracture: uneven. Chemical: insoluble in strong mineral acids, but attacked by HCl after calcination giving
a gel of silica, fusible giving a dark green globule. Occurrence: regional metamorphic and
pegmatite rocks.
