Sepiolite

Sepiolite, also known in English by the German loanword meerschaum ( , ; German:; meaning "sea foam"), is a soft white clay mineral, often used to make tobacco pipes (known as meerschaum pipes). A complex magnesiumsilicate, a typical chemical formula for which is Mg₄Si₆O₁₅(OH)₂·6H₂O, it can be present in fibrous, fine-particulate, and solid forms.

The fibrous clay minerals have been shown to exist as a continuous polysomatic series where the endmembers are sepiolite and palygorskite; there is a continuous variation in chemical composition from sepiolite, the most magnesic and trioctahedral endmember, to palygorskite, the least magnesic, most Al- and Fe-bearing, most dioctahedral endmember.

Originally named Meerschaum by Abraham Gottlob Werner in 1788, it was named sepiolite by Ernst Friedrich Glocker in 1847 for an occurrence in , Baldissero Canavese, Torino Province, Piedmont, Italy. The name comes from Greeksepion (σήπιον), meaning "cuttlebone" (the porous internal shell of the cuttlefish), + lithos (λίθος), meaning stone, after a perceived resemblance of this mineral to cuttlebone. Because of its low relative density and its high porosity, it may float upon water, hence its German name: 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 of the French name for the same substance, écume de mer.