Palygorskite - (Mg,Al)₂Si₄O₁₀(OH)·4H₂O

Habit: White, grayish, yellowish or gray green. Crystals tiny laths; commonly fibrous, forming tangled mats termed "mountain leather"; also compact. Earthy to waxy luster; semitransparent. White streak.

Environment: An alteration product of magnesium silicates in soils and sediments; in lacustrine marls, carbonate rocks and mafic igneous rocks; and in clay gouge associated with fault movement.

Etymology: Named for its type locality, Palygorskaya, in the Perm district of the Ural Mountains in Russia.