1911 Encyclopædia Britannica/Spodumene
|←Splügen Pass|| 1911 Encyclopædia Britannica, Volume 25
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SPODUMENE, a lithium-aluminium silicate belonging to the pyroxene group (see Pyroxene). It was named by B. J. d'Andrada e Sylva, in 1800, from Gr. σπóδιος (ash-coloured), in allusion to its grey colour. Soon afterwards J. R. Haüy termed it triphane, because it exhibited certain characteristics equally in three directions (τριφανής, appearing three-fold). Spodumene crystallizes in the monoclinic system, the crystals having generally a prismatic habit and being often striated longitudinally. It has perfect prismatic cleavage, and imperfect cleavage parallel to the clinopinacoid, whilst a lamellar structure may be developed by parting along the orthopinacoid. The hardness is 6.5 to 7, and the specific gravity about 3.16. Though generally a dull mineral, some varieties of spodumene are so brightly coloured and transparent as to be valued as gem-stones. Such is the emerald-green hiddenite (q.v.) and the lilac-coloured kunzite (q.v.), whilst a yellow or yellowish-green spodumene found as pebbles in the state of Minas Geraes, in Brazil, resembles, when cut, some kinds of chrysoberyl. Common spodumene is used as a source of lithium in chemical preparations.
Spodumene occurs in granite and crystalline schists. The original specimens came from the isle of Utö in Södermanland, Sweden, but the finest examples are found in the United States, especially in Massachusetts, where Goshen, Sterling and Chesterfield are well-known localities. Very fine specimens have been obtained from the Black Hills of S. Dakota. Some remarkable deposits containing spodumene were discovered many years ago at Branchville, Fairfield county, Connecticut, and the minerals which they yielded were exhaustively studied by Professor G. J. Brush and E. S. Dana. The spodumene occurred in large quantity, in a vein of albite-granite, associated with apatite, garnet, columbite, pitchblende and other uranium minerals, together with several species of manganese phosphates, termed eosphorite, triploidite, dickinsonite, lithiophilite, natrophilite, reddingite, fairfieldite and fillowite. The spodumene, which has normally the formula LiAl(SiO3)2, becomes altered at Branchville to what has been called β-spodumene, which consists really of the mineral eucryptite (LiAlSiO4) and albite. Eucryptite was named by Brush and Dana from εὖ (well) and κρυπτóς (concealed). Further alteration results in the formation of cymatolite, a mineral described by C. U. Shepard in 1867, but shown to be an intimate mechanical mixture of muscovite and albite. The final products of alteration of the spodumene may be muscovite, albite and microcline. The mineral discovered in 1817 in the granite of Killiney Hill, near Dublin, and described by T. Thomson as killinite, appears to be an altered spodumene. (F. W. R.*)