Formula: Mg4Si6O15(OH)2.6H2O
Phyllosilicate (sheet silicate)
Specific gravity: 2.0 to 2.2
Hardness: 2
Streak: White
Colour: White, light grey or light yellow
Common impurities: Al,Ca,Fe,Ni


Sepiolite is a secondary clay mineral associated with serpentine. It can precipitate from alkali saline waters in arid environments (Webmin). Sepiolite is an alteration product of both serpentine and magnesite (Dana). Associated minerals include opal, dolomite and palygorskite (HOM, Dana).


In the evaporite basins of the Mallee District, Murray Basin, south-eastern Australia, sepiolite has been found with halite and gypsum in the organic mud beneath the upper crust of the salt pans. A fragment of sepiolite has also been reported associated with common opal in the clay formation at Nampoo Station, near Lake Victoria, New South Wales. (AJM 10.1.23).

The type locality is Monti Pelati, Bettolino, Baldissero Canavese, Metropolitan City of Turin, Piedmont, Italy.

At the Cerro de Mercado Mine, Victoria de Durango, Durango Municipality, Durango, Mexico, sepiolite is commonly found filling voids, in some cases overgrown by quartz crystals (Minrec 42.5.485).

At Creastmore, Riverside county, California, USA, sepiolite occurs in small veins in calcite and as pellets in limestone (Dana).

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