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Sepiolite - sepiolit.jpg
A sample of sepiolite
Category Phyllosilicates
(repeating unit)
Strunz classification 09.EE.25 Single tetrahedral nets of 6-membered rings
Dana classification 74.03.01b.01 Palygorskite-sepiolite group
Crystal symmetry Orthorhombic 2/m2/m2/m
Unit cell a = 5.21 Å, b = 26.73 Å, c = 13.5 Å; Z = 4
Color Grayish white, white, white with a yellowish or reddish tinge; bluish green
Crystal habit Compact nodular, earthy, clayey, massive; rarely fine fibrous along [001]
Crystal system Orthorhombic - Dipyramidal
Mohs scale hardness 2
Luster Dull, earthy
Streak White
Diaphaneity Opaque
Specific gravity 2; dry porous masses float on water
Optical properties Biaxial (-)
Refractive index nα = 1.520 nβ = 1.520 nγ = 1.530
Birefringence δ = 0.010
2V angle Measured: 20° to 70°, Calculated: 18°
References [1][2][3]

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.

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.[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.[citation needed] Careful analytical techniques may be required to distinguish the two.


Sepiolite is used in oil drilling, for cat litter and in a solid form for carving of items, where it is known as meerschaum. In construction, sepiolite can be used in lime mortars as water reservoir.[4][5]


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