A magnesium silicate
The silicate, known as sepiolite, is a fine, soft, off-white clay mineral with low specific gravity, and is highly porous. It is sometimes found floating on the surface of the sea, resembling foam, hence its German name of meerschaum, meaning sea foam. It hardens on exposure to the sun's heat or when dried in the warm. Its main modern use has been as absorbent, cool, easily carved pipe bowls.
