Meerschaum also sepiolite

Sepiolite

Sepiolite is a clay mineral, a complex magnesium silicate, a typical formula for which is Mg4Si6O152·6H2O. It can be present in fibrous, fine-particulate, and solid forms....

, is a soft white mineral

Mineral

A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

 sometimes found floating on the Black Sea

Black Sea

The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...

, and rather suggestive of sea-foam, whence the German origin of the name, as well as the French name for the same substance, écume de mer.
Meerschaum is opaque and of white, grey or cream color, breaking with a conchoidal or fine earthy fracture, and occasionally fibrous in texture. Because it can be readily scratched with the nail, its hardness is placed at about 2.