Taken from wiki:
Meerschaum, German for foam of the sea), also known as sepiolite,[1] is a soft white mineral, often used to make smoking pipes. It is sometimes found floating on the Black Sea and rather suggestive of sea-foam, hence the German origin of the name as well as the French name for the same substance, écume de mer.
Sepiolite is a clay mineral, a complex magnesium silicate, a typical formula for which is Mg4Si6O15(OH)2·6H2O. It can be present in fibrous, fine-particulate, and solid forms.
It was first described in 1847 for an occurrence in Bettolino, Baldissero Canavese, Torino Province, Piedmont, Italy. The name comes from a perceived resemblance of the material to the porous bones of the cuttlefish from the Greek, "sepion".[2] Because of its low specific gravity and its high porosity it may float upon water, hence its German name meerschaum ("sea foam").
Sepiolite occurs as a secondary mineral associated with serpentine. It can occur as a precipitate in arid environments. It may be associated with dolomite and opal.[1][3]
Owing to its fibrous mineral nature, sepiolite veins may contain the hazardous material, asbestos; even where asbestos is not present, sepiolite is often mistaken for it. Careful analytical techniques may be required to distinguish the two.