Sepiolite - Mg₄Si₆O₁₅(OH)₂·6H₂O

Habit: White, light gray or light yellow. Compact nodular, earthy, clayey or massive; rarely fine fibrous. Dull luster; opaque. White streak.

Environment: A sedimentary clay mineral also found in serpentine.

Etymology: From the Greek sepion, meaning "cuttlefish bone," because of its low density and porous, bonelike appearance.