Hectorite

Hectorite
Hectorite from California
General
Category	Phyllosilicate minerals
Group	Smectite group
Formula	Na0.3(Mg,Li)3Si4O10(OH)2 (empirical: Na3(Mg,Li)30Si40O100(OH)20)
IMA symbol	Htr1
Strunz classification	9.EC.45
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/m
Unit cell	a = 5.25 Å, b = 9.18 Å c = 16 Å; β = 99°; Z = 2
Identification
Color	White, cream, pale brown, mottled
Crystal habit	Thin laths and aggregates
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	234

Hectorite is a rare soft, greasy, white, lithium-rich clay mineral with a chemical formula of Na_0.3(Mg,Li)₃Si₄O₁₀(OH)₂.²

Hectorite was first described in 1941 and named for an occurrence in the United States near Hector, California (in San Bernardino County, California,⁴ 30 miles east of Barstow). Hectorite belongs to the smectite group; it is a swelling 2:1 clay mineral. Hectorite occurs with bentonite as an alteration product of clinoptilolite from volcanic ash and tuff with a high glass content.² Hectorite is also found in the beige/brown clay ghassoul, mined in the Atlas Mountains in Morocco.⁵ A large deposit of hectorite is also found at the Thacker Pass lithium deposit, located within the McDermitt Caldera in Nevada. The Thacker Pass lithium deposit could be a significant source of lithium.⁶

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.⁷