Sépiolite

Sepiolite, also known in English by the German name meerschaum (ˈmɪərʃɔːm , -ʃəm ; ˈmeːɐ̯ʃaʊm; meaning "sea foam"), is a soft white clay mineral, often used to make tobacco pipes (known as meerschaum pipes). A complex magnesium silicate, 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 recently 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- Fe- bearing, 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 Bettolino, Baldissero Canavese, Torino Province, Piedmont, Italy. The name comes from Greek sepion (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 the French name for the same substance, écume de mer. Sepiolite is opaque and off-white, grey or cream colour, breaking with a conchoidal or fine earthy fracture, and occasionally fibrous in texture. Due to the fact it can be readily scratched with the finger nail, its hardness is ranked at about 2 on the Mohs scale. The specific gravity varies from 0.988 to 1.279, but the porosity of the mineral may lead to error. Sepiolite is a hydrous magnesium silicate having the chemical formula Mg4Si6O15(OH)2·6H2O. Sepiolite can be identified in hand specimen by applying a drop of a saturated solution of methyl orange on the sample. A positive test result for sepiolite turns purple.