spodumene

n.
A greenish to pinkish or lilac mineral, LiAlSi₂O₆, used as a source of lithium and in transparent varieties as a gemstone.

[French spodumène, from German Spodumen, from Greek spodoumenos, present participle of spodousthai, to be burned to ashes, from spodos, wood ashes (because the mineral becomes ash gray when exposed to air).]

The name given to the monoclinic lithium pyroxene LiAl(SiO₃)₂. Spodumene commonly occurs as white to yellowish prismatic crystals, often with a “woody” appearance.

Spodumene is usually found as a constituent in certain granitic pegmatites. The emerald-green variety, hiddenite, and a lilac variety, kunzite, are used as precious stones. Spodumene from pegmatites is used as an ore for lithium. See also Lithium; Pyroxene.

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LiAlSi
Monoclinic -- prismatic

Environment

Almost exclusively a pegmatite mineral.

Crystal description

Usually in elongated, embedded feldspar-like crystals, commonly well developed. Free-growing examples are characterized by striated prism and pinacoid faces and steep terminations. Very large (40 ft.; 10 m) crystals have been described in South Dakota. Networks of intergrowing crystals may not show any terminations. Very susceptible to attack by late-phase alkaline solutions and commonly deeply etched and pitted. Also smaller and gemmy in lithium pegmatite pockets.

Physical properties

Opaque varieties buff, white, lavender, greenish; transparent varieties colorless, lilac, (kunzite), yellow (triphane), pale green (Brazil), and -- in North Carolina only -- emerald green (hiddenite). Luster glassy; hardness 6Ɖ-7; specific gravity 3.1-3.2; fracture uneven, rather tough and splintery across prism directions; cleavage perfect prismatic 87° and 93° good partings parallel to front pinacoid. Transparent to translucent; thermoluminescent, often fluorescent under ultraviolet followed by a brilliant and persistent phosphorescence in orange.

Composition

Lithium aluminum silicate (8.0% Li ₂ O, 27.4% Al ₂ O ₃ , 64.6% SiO ₂ ).

Tests

Fuses to a clear glass after developing small zeolite-like protuberances, while coloring the flame bright red (lithium). On initial heating will show marked thermoluminescence. Fluoresces orange, seen best in longwave ultraviolet or in x-rays; fused material fluoresces blue in shortwave ultraviolet. Fresh from the mine and kept in the dark it may be bluish or greenish, but heat or exposure to light changes it to a normal kunzite violet, which seems to the stable hue (though inclined to fade a little in time). Brilliantly phosphorescent after irradiation, giving in daylight to a careless observer the illusion of a short-lived brownish color, before showing its normal greenish irradiation hue which eventually reverts to lilac.

Distinguishing characteristics

The pegmatitic occurrence, the common association with other lithium minerals, such as lepidolite mica and elbaite tourmalines, is usually sufficient. A tough splintery fracture distinguishes opaque cleavages from feldspar. Distinctive in many ways, including its luminescent qualities.

Occurrence

Found only where there are lithium-rich pegmatites, and it is usually, though not always, associated with lepidolite, bright-hued elbaite tourmaline, cesium beryl, amblygonite, and/or herderite.

The transparent colored varieties have value as gems; the ordinary material was an important ore of lithium. Lithium pegmatites are found in New England -- notably in Maine, Connecticut, and Massachusetts. The usual lithium mineral associates are absent at the commercially mined deposit of Kings Mountain, North Carolina. The Hiddenite (Alexander Co., North Carolina) locality is unusual because the small green gem (hiddenite) crystals occur in alpine-type seams in gneiss and must have been deposited largely from solutions, rather than from magma.

Good crystals are found at Dixon, New Mexico and in the Black Hills of South Dakota, especially at the Etta Mine, where the mammoth crystals mentioned above were mined. Gemmy lilac crystals (kunzite) are found in several San Diego Co. pegmatites in the vicinity of Pala, California. Elsewhere in the world spodumene is found in Minas Gerais, Paraíba, and Rio Grande do Norte, Brazil; Madagascar; Namibia; and Varütrask, Sweden. Kunzite in abundance has also come from Urupuca, Minas Gerais, Brazil. In this decade, Pakistan and Afghanistan have flooded the market with the freshest, least etched, and most spectacular crystals to date.

Remarks

The massive ore-type of spodumene alters easily to greenish mica pseudomorphs ("pinite") or to clay pseudomorphs after the crystals. Gemmy crystals are frequently traversed by long curving slender tubes that start from the bottom of etch pits on the crystal surface, ending in like and opposite pits. Except for the abundant Afghanistan finds, clear spodumene from other sources is invariably so etched so that the original surface of the faces has been lost.

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The noun has one meaning:

Meaning #1: a pyroxene mineral consisting of lithium aluminum silicate; a source of lithium

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