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Hectorite from California
Category Phyllosilicates
(repeating unit)
(empirical: Na3(Mg,Li)30Si40O100(OH)20)
Strunz classification 09.EC.45
Crystal symmetry Monoclinic prismatic
H-M symbol: (2/m)
Space group: C 2/m
Unit cell a = 5.25 Å, b = 9.18 Å, c = 16 Å; β = 99°
Color White, cream, pale brown, mottled
Crystal habit Thin laths and aggregates
Crystal system Monoclinic
Cleavage [001] Perfect
Fracture Uneven
Mohs scale hardness 1 - 2
Luster Earthy to waxy
Streak White
Diaphaneity Translucent to opaque
Specific gravity 2-3
Optical properties Biaxial (-) - 2V small
Refractive index nα = 1.490 nβ = 1.500 nγ = 1.520
Birefringence δ = 0.030
References [1][2][3]

Hectorite is a rare soft, greasy, white clay mineral with a chemical formula of Na0.3(Mg,Li)3Si4O10(OH)2.[1]

Hectorite was first described in 1941 and named for an occurrence in the United States near Hector (in San Bernardino County, California,[3] 30 miles east of Barstow.) Hectorite occurs with bentonite as an alteration product of clinoptilolite from volcanic ash and tuff with a high glass content.[1] Hectorite is also found in the beige/brown clay ghassoul, mined in the Atlas Mountains in Morocco.[4]

Despite its rarity, it is economically viable as the Hector mine sits over a large deposit of the mineral. Hectorite is mostly used in making cosmetics, but has uses in chemical and other industrial applications, and is a mineral source for refined lithium metal.[5]


  1. 1.0 1.1 1.2 Handbook of Mineralogy
  2. Hectorite data on Webmineral
  3. 3.0 3.1 Ralph, Jololyn and Ida (2007): Hectorite on Mindat.org
  4. Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).
  5. Moores, Simon (2007) Between a rock and a salt lake; Industrial Minerals, June '07