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]}

Spodumene was first described in 1800 for an occurrence in the type locality in Utö, Södermanland, Sweden. It was discovered by Brazilian naturalist Jose Bonifacio de Andrada e Silva. The name is derived from the Greek spodumenos (σποδούμενος), meaning "burnt to ashes", owing to the opaque ash-grey appearance of material refined for use in industry.^[2]

Spodumene occurs in lithium-rich granite pegmatites and aplites. Associated minerals include: quartz, albite, petalite, eucryptite, lepidolite and beryl.^[3]

Transparent material has long been used as a gemstone with varieties kunzite and hiddenite noted for their strong pleochroism. Source localities include Democratic Republic of Congo, Afghanistan, Australia, Brazil, Madagascar (see mining), Pakistan, Québec in Canada, and North Carolina and California in the U.S.

Since 2018, the Democratic Republic of Congo (DRC) has been known to have the largest lithium spodumene hard rock deposit in the world, with mining operations occurring in the central DRC territory of Manono, Tanganyika Province.^[8] As of 2021, the Australian company AVZ Minerals^[9] is developing the Manono Lithium and Tin project and has a resource size of 400 million tonnes of high grade low impurities at 1.65% lithium oxide (Li₂O)^[10] spodumene hard-rock based on studies and drilling of Roche Dure, one of several pegmatites in the deposit.

Spodumene is an important source of lithium, for use in ceramics, mobile phones and batteries (including for automotive applications), medicine, Pyroceram and as a fluxing agent. As of 2019, around half of lithium is extracted from mineral ores, which mainly consist of spodumene. Lithium is recovered from spodumene by dissolution in acid, or extraction with other reagents, after roasting to convert it to the more reactive β-spodumene. The advantage of spodumene as a lithium source compared to brine sources is the higher lithium concentration, but at a higher extraction cost.^[11]

In 2016, the price was forecast to be $500–600/ton for years to come.^[12] However, price spiked above $800 in January 2018, and production increased more than consumption, reducing the price to $400 in September 2020.^[13][14]

World production of lithium via spodumene was around 80,000 metric tonnes per annum in 2018, primarily from the Greenbushes pegmatite of Western Australia and from some Chinese and Chilean sources. The Talison Minerals mine in Greenbushes, Western Australia (involving Tianqi Lithium, Albemarle Corporation and Global Advanced Metals), is reported to be the world's second largest and to have the highest grade of ore at 2.4% Li₂O (2012 figures).^[15]

In 2020, Australia expanded spodumene mining to become the leading lithium producing country in the world.^[16]

An important economic concentrate of spodumene, known as spodumene concentrate 6 or SC6, is a high-purity lithium ore with approximately 6 percent lithium content being produced as a raw material for the subsequent production of lithium-ion batteries for electric vehicles.^[17][18]

Extraction of lithium from spodumene, often spodumene concentrate 6 (SC6), is challenging due to the tight binding of lithium in the crystal structure.

Traditional lithium refining in the 2010s involves acid leaching of lithium-containing ores, precipitation of impurities, concentration of the lithium solution, and then conversion to lithium carbonate or lithium hydroxide. These refining methods result in significant quantities of caustic waste effluent and tailings, which are usually either highly acidic or alkali.^[11]

Another processing method relies on pyrometallurgical processing of SC6—roasting at high temperatures exceeding 800 °C (1,470 °F) to convert the spodumene from the tightly-bound alpha structure to a more open beta structure from which the lithium is more easily extracted—then cooling and reacting with various reagents in a sequence of hydrometallurgical processing steps. Some offer the use of non-caustic reagents and result in reduced waste streams, potentially allowing the use of a closed-loop refining process.^[19]

Suitable extraction reagents include alkali metal sulfates, such as sodium sulfate; sodium carbonate; chlorine; or hydrofluoric acid.^[20] A common form of more highly refined lithium is lithium hydroxide, commonly used as an input in the battery industry to manufacture lithium-ion (Li-ion) battery cathode material.

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Hiddenite is a pale, emerald-green gem variety first reported from Alexander County, North Carolina, U.S.^[21] It was named in honor of William Earl Hidden (16 February 1853 – 12 June 1918), mining engineer, mineral collector, and mineral dealer.^{[22][additional citation(s) needed]}

This emerald-green variety of spodumene is colored by chromium, just as for emeralds. Some green spodumene is colored with substances other than chromium; such stones tend to have a lighter color; they are not true hiddenite.

Kunzite is a purple-colored gemstone, a variety of spodumene, with the color coming from minor to trace amounts of manganese. Exposure to sunlight can fade its color.^[22]

Kunzite was discovered in 1902, and was named after George Frederick Kunz, Tiffany & Co's chief jeweler at the time, and a noted mineralogist.^[22] It has been found in Brazil, the U.S., Canada, CIS, Mexico, Sweden, Western Australia, Afghanistan and Pakistan.^[22][23]

• 
  An almost colorless kunzite crystal (upper left), a cut pale pink kunzite (upper right) and a greenish hiddenite crystal (below) (unknown scale)
• 
  Kunzite, Nuristan Province, Afghanistan
• 
  Hiddenite from Araçuaí, Minas Gerais, Brazil

Triphane is the name used for yellowish varieties of spodumene.^[24]

• List of minerals

• Kunz, George Frederick (1892). Gems and Precious Stones of North America. New York: The Scientific Publishing Company.
• Palache, C., Davidson, S. C., and Goranson, E. A. (1930). "The Hiddenite deposit in Alexander County, N. Carolina". American Mineralogist Vol. 15 No. 8 p. 280
• Webster, R. (2000). Gems: Their Sources, Descriptions and Identification (5th ed.), pp. 186–190. Great Britain: Butterworth-Heinemann.
• The key players in Quebec lithium Archived 2013-01-30 at archive.today, "Daily News", The Northern Miner, 11 August 2010.

Wikimedia Commons has media related to Spodumene.

• Texts on Wikisource:
  • "Kunzite". Encyclopædia Britannica (11th ed.). 1911.
  • Rudler, Frederick William (1911). "Spodumene". Encyclopædia Britannica (11th ed.).
  • "Spodumene". New International Encyclopedia. 1905.