Spodumene

Spodumene
Walnut Hill Pegmatite Prospect, Huntington, Hampshire County, Massachusetts, USA (Size: 14.2 x 9.2 x 3.0 cm)
General
Category	Silicate mineral, pyroxene
Formula (repeating unit)	lithium aluminium silicate, LiAl(SiO3)2
Crystal symmetry	Monoclinic 2/m
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
Crystal habit	prismatic, generally flattened and elongated, striated parallel to {100}, commonly massive
Crystal system	Monoclinic; 2/m
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, kunzite often fluorescent under UV[citation needed]
References	[1][2][3][4]

Spodumene is a pyroxene mineral consisting of lithium aluminium inosilicate, LiAl(SiO₃)₂, and is a 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.^[5]
The normal low-temperature form α-spodumene is in the monoclinic system whereas the high-temperature β-spodumene crystallizes in the tetragonal system. The normal α-spodumene converts to β-spodumene at temperatures above 900 °C.^[4] Crystals are typically heavily striated parallel to the principal axis. Crystal faces are often etched and pitted with triangular markings.

Discovery and occurrence

Spodumene was first described in 1800 for an occurrence in the type locality in Utö, Södermanland, Sweden. The name is derived from the Greek spodumenos (σποδυμενος), meaning "burnt to ashes," owing to the opaque, ash-grey appearance of material refined for use in industry.^[1]
Spodumene occurs in lithium-rich granite pegmatites and aplites. Associated minerals include: quartz, albite, petalite, eucryptite, lepidolite and beryl.^[2]
Transparent material has long been used as a gemstone with varieties kunzite and hiddenite noted for their strong pleochroism. Source localities include Afghanistan, Australia, Brazil, Madagascar, Pakistan, Québec in Canada and North Carolina, California in the USA.

Economic importance

Spodumene is an important source of lithium for use in ceramics, mobile phone and automotive batteries, medicine and as a fluxing agent. Lithium is extracted from spodumene by fusing in acid.
World production of lithium via spodumene is around 80,000 metric tonnes per annum, primarily from the Greenbushes pegmatite of Western Australia, and some Chinese and Chilean sources. The Talison mine in Greenbushes, Western Australia has an estimated reserve of 13 million tonnes.^[6]
Some think that spodumene will become a less important source of lithium due to the emergence of alkaline brine lake sources in Chile, China and Argentina, which produce lithium chloride directly. Lithium chloride is converted to lithium carbonate and lithium hydroxide by reaction with sodium carbonate and calcium hydroxide respectively.
But, pegmatite-based projects benefit from being quicker to move into production than brines, which can take 18 months to 3 years, depending on evaporation rates. With pegmatites, once a mill is built, the production of lithium carbonate is only a matter of days.
Another key advantage that spodumene has over its more popular brine rivals, is the purity of the lithium carbonate it can produce. While all product used by the battery industry have to grade at least 99.5% lithium carbonate, the make up of that final 0.5% is important. If it contains higher amounts of iron, magnesium or other deleterious materials it is less attractive to end users.

Gemstone varieties

Hiddenite

Hiddenite is a pale emerald green gem variety first reported from Alexander County, North Carolina, U. S. A.
This emerald green variety of spodumene is colored by chromium, just like emeralds. Not all green spodumene is colored with chromium, which tend to have a lighter color, and therefore are not true hiddenite.

Kunzite

Kunzite is a pink to lilac colored gemstone, a variety of spodumene with the color coming from minor to trace amounts of manganese. Some (but not all) kunzite used for gemstones has been heated to enhance its color. It is also frequently irradiated to enhance the color. Many kunzites fade when exposed to sunlight.
Kunzite was discovered in 1902, and was named after George Frederick Kunz, Tiffany & Co's chief jeweler at the time, and a noted mineralogist. It has been found in Brazil, USA, Canada, CIS, Mexico, Sweden, Western Australia, Afghanistan and Pakistan.
One notable example of kunzite used in jewellery is in the Russian Palmette tiara and necklace worn by the Duchess of Gloucester.^[7]

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  An almost colorless kunzite crystal (upper left), a cut pale pink kunzite (upper right) and a greenish hiddenite crystal (below) (unknown scale)
  
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  Kunzite Nouristan