Spodumene

Spodumene
Walnut Hill Pegmatite Prospect, Huntington, Hampshire County, Massachusetts, U.S. (size: 14.2 × 9.2 × 3.0 cm)
General
Category	Inosilicate
Formula (repeating unit)	lithium aluminium silicate, LiAl(SiO3)2
IMA symbol	Spd[1]
Strunz classification	9.DA.30
Dana classification	65.1.4.1
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/c
Unit cell	a = 9.46 Å, b = 8.39 Å c = 5.22 Å β = 110.17°; Z = 4
Identification
Color	Highly variable: white, colorless, gray, pink, lilac, violet, yellow and green, may be bicolored; emerald green – hiddenite; lilac – kunzite; yellow – triphane
Crystal habit	prismatic, generally flattened and elongated, striated parallel to {100}, commonly massive
Twinning	Common on {100}
Cleavage	Perfect prismatic, two directions {110} ∧ {110} at 87°
Fracture	Uneven to subconchoidal
Tenacity	Brittle
Mohs scale hardness	6.5–7
Luster	Vitreous, pearly on cleavage
Streak	white
Specific gravity	3.03–3.23
Optical properties	Biaxial (+)
Refractive index	nα = 1.648–1.661 nβ = 1.655–1.670 nγ = 1.662–1.679
Birefringence	δ = 0.014–0.018
Pleochroism	Strong in kunzite: α-purple, γ-colorless; hiddenite: α-green, γ-colorless
2V angle	54° to 69°
Fusibility	3.5
Solubility	insoluble
Other characteristics	Tenebrescence, chatoyancy
References	[2][3][4][5]

Spodumene is a pyroxene mineral consisting of lithium aluminium inosilicate, LiAl(SiO₃)₂, and is a commercially important source of lithium. It occurs as colorless to yellowish, purplish, or lilac kunzite (see below), yellowish-green or emerald-green hiddenite, prismatic crystals, often of great size. Single crystals of 14.3 m (47 ft) in size are reported from the Black Hills of South Dakota, United States.^[6][7]

The naturally-occurring low-temperature form α-spodumene is in the monoclinic system, and the high-temperature β-spodumene crystallizes in the tetragonal system. α-spodumene converts to β-spodumene at temperatures above 900 °C.^[5] Crystals are typically heavily striated parallel to the principal axis. Crystal faces are often etched and pitted with triangular markings.^{[not verified in body]}