Sunday, July 19, 2009

Spodumene

Spodumene

"Kunzite" redirects here. For the Sailor Moon character, see Shitennou.
Spodumene

An almost colorless kunzite crystal (upper left), a cut pale pink kunzite (upper right) and a greenish hiddenite crystal (below) (unknown scale)
General
CategoryMineral
Chemical formulalithium aluminium silicate, LiAl(SiO3)2
Identification
ColorHighly variable: white, colorless, gray, pink, lilac, violet, yellow and green
Crystal habitprismatic, generally flattened and elongated
Crystal systemmonoclinic; 2/m
CleavagePerfect prismatic, two directions at nearly 90°
FractureSub-conchoidal
Mohs Scalehardness6.5 - 7
LusterVitreous
Streakwhite
Specific gravity3.17-3.19
Refractive index1.66-1.68
PleochroismStrong in kunzite: pink, colorless; hiddenite: yellow-green, blue-green
Fusibility3.5
Solubilityinsoluble
Other characteristicsTenebrescence, chatoyancy, kunzite often fluorescentunder UV

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 in size are reported from the Black Hills of South Dakota, United States.[1]

Crystals form in the monoclinic system and are typically heavily striated parallel to the principal axis. Crystal faces are often etched and pitted with triangular markings.

Spodumene 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.

Spodumene occurs in lithium rich granites and pegmatites. Transparent material has long been used as a gemstone with varieties kunzite and hiddenite noted for their strongpleochroism. Source localities include Afghanistan, Australia, Brazil, Madagascar, Pakistanand USA (North Carolina, California).


Economic importance

Spodumene is an important source of lithium for use in ceramics, mobile phone andautomotive 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 andChilean sources. The Talison mine in Greenbushes, Western Australia has an estimated reserve of 13 million tonnes.[2]

Spodumene is becoming less important a source of lithium due to the emergence of alkalinebrine lake sources in Chile, China and Argentina, which produce lithium chloride directly. Lithium chloride is converted to lithium carbonate and lithium hydroxide by reaction withsodium carbonate and calcium hydroxide respectively.

Kunzite

Kunzite
See the pleochroism and the typical etched marks (unknown scale)
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. It 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.

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