An important source of high-purity lithium and a gemstone with collector appeal
What is Spodumene?
Spodumene is a pyroxene mineral that is found, almost exclusively, in granite pegmatites. It has a chemical composition of LiAlSi2O6 but small amounts of sodium sometimes substitute for lithium. Spodumene is typically found in lithium-rich pegmatites in association with other lithium minerals such as lepidolite, eucryptite, and petalite. In the historical literature, the mineral is often referred to as "triphane."
Physical Properties of Spodumene
|Color||White, gray, yellow, green, blue, lilac, pink, brown. Sometimes pleochroic|
|Diaphaneity||Transparent to translucent|
|Cleavage||Perfect in two directions with parting|
|Mohs Hardness||6.5 to 7|
|Specific Gravity||3.1 to 3.3|
|Diagnostic Properties||Prismatic crystals with strong striations parallel to their principal axis. Perfect cleavage.|
|Crystal System||Monoclinic (low temperature), tetragonal (high temperature)|
|Uses||An ore of lithium. Gemstones (kunzite, hiddenite)|
Spodumene often occurs in extremely large crystals. One of the earliest accounts of large spodumene crystals is from the Etta Mines, Black Hills, Pennington County, South Dakota. The United States Geological Survey, Bulletin 610 reports:
"The crystals are often of enormous size. In the Etta Mine, where they are best exposed both in the open cut and tunnel, they frequently attain a diameter of 3 to 4 feet and a length of 30 feet. The largest "log" so far found was 42 feet long and 5 feet 4 inches in maximum diameter. This one log alone would yield 90 tons of spodumene." 
Uses of Spodumene
Spodumene once served as the most important ore of lithium metal. Although it remains an important source of lithium, today most of the world's lithium is produced from subsurface brines in Chile, Argentina, and China. These sources of lithium have lower production costs and are suitable for most uses. However, when lithium of highest purity is needed, spodumene is the source that is used.
Spodumene as a Gemstone
Spodumene sometimes occurs in transparent crystals in pastel shades of pink, green, and yellow. These have been cut into gemstones that are prized by collectors. However, their use in jewelry is limited to pieces that will be subject to limited abuse because of spodumene's perfect cleavage.
Pink to lilac specimens of gem-quality spodumene are highly prized and known as "kunzite". The color of these specimens is attributed to the presence of manganese as a chromophore. Kunzite is the most commonly encountered spodumene gem.
Many specimens of kunzite are strongly pleochroic, with the deepest color observed when the gem is viewed down the principal axis. To take full advantage of its phenomenon, gemstones are cut with the table perpendicular to the principal axis to yield stones of the deepest color.
Some kunzite will develop a richer color when heated or irradiated. These procedures have been applied to some stones that enter the marketplace. Some specimens of kunzite will fade over time when exposed to direct sunlight. Valuable stones should be stored away from direct light and, to be conservative, in a closed container.
Emerald-green spodumene is known as "Hiddenite." Its vivid green color is very similar to emerald and is attributed to the presence of chromium as a chromophore. It is the rarest gem variety of spodumene. It was first found near the town of Stony Point, North Carolina, which changed its name to "Hiddenite" after the popular gemstone that attracted people to the area.
Yellow and clear specimens of spodumene have also been cut into gems; however, variety names for spodumene gems have only been given to Kunzite and Hiddenite.
|Did You Know? Lithium is an active ingredient in some medications. Salts of lithium are used in medication for bipolar disorder. The lithium contributes to a "mood-stabilizing" effect. One product has been named "Lithium." Image © iStockphoto / Paige Foster.|
Demand for Spodumene
The demand for spodumene is dependent upon the use of lithium in manufacturing. In the past, most lithium compounds and minerals were used to produce ceramics, glass, aluminum alloys, and high-temperature grease. However, an exploding demand for rechargeable batteries to power cell phones, tablet computers, cameras, music players, GPS units, and other portable electronic devices is driving the demand for high-purity lithium - and that drives the demand for spodumene.
Lithium batteries have a much higher charge-to-weight ratio and power-to-weight ratio than lead/acid and zinc carbon cells. This makes lithium the battery material of choice.
Lithium produced from spodumene has fewer contaminants than lithium produced from brines. These contaminants can interfere with battery performance and make spodumene the preferred choice for battery lithium. A new battery technology could displace the use of lithium; however, most new battery technologies have been lithium-based.
Author: Hobart M. King, Ph.D.
 Mineralogic Notes, Series 3: Waldemar Schaller, Gigantic Crystals of Spodumene, United States Geological Survey, Bulletin 610, 1916. |
 Lithium: Brian Jaskula, United States Geological Survey, Mineral Commodity Summaries, January 2012.
 Lithium: Brian Jaskula, United States Geological Survey, Minerals Yearbook, December 2011.
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