polyhalite

Habit: massive, lamellar, fibrous.
Color: white, yellowish white, gray, or flesh pink.
Luster: vitreous (glassy).
Streak: white.
Cleavage: [101] perfect.
Fracture: conchoidal, brittle.
Occurrence: sedimentary marine evaporite deposits.

Source of potash for fertilizer.

A naturally occurring potash salt found in Germany,Texas, and New Mexico.