Formula: Mg4Si6O15(OH)2.6H2O
Phyllosilicate (sheet silicate), sepiolite group
Crystal System: Orthorhombic
Specific gravity: 2.0 to 2.2 measured, 2.25 calculated
Hardness: 2
Streak: White
Colour: White, light grey or light yellow
Common impurities: Al,Ca,Fe,Ni
Environments
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).
Localities
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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