Online Encyclopedia

SPHENE

Online Encyclopedia
Originally appearing in Volume V25, Page 647 of the 1911 Encyclopedia Britannica.
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SPHENE, a mineral consisting of calcium titan-silicate, CaTiSiO5, crystallizing in the monoclinic system. The crystals vary considerably in habit, but are generally thin and wedge-shaped; hence the name sphene, from the Greek a¢ v (a wedge), given by R. J. Hauy in 18or. The earlier name titanite, given by M. H. Klaproth in 1795, is also in common use. Twinning on the ortho-pinacoid is not uncommon. The colour is green, yellow, brown or black, and the lustre resinous to adamantine; crystals are transparent to opaque. The hardness is 51, and the specific gravity 3.5. The refractive indices and the optic axial angle vary considerably with the colour of the light: the dispersion of the optic axes is inclined, and the interference figure seen in convergent light between crossed nicols is very characteristic of the mineral. Sphene is sometimes cut as a gem-stone, though it is rather too soft to stand much wear; owing to its high dispersive power it gives brilliant flashes of prismatic colours. As small embedded crystals, sphene has a wide distribution as an accessory constituent of many kinds of igneous rocks (granite, syenite, trachyte, phonolite, &c.), and also of gneiss, schist and crystalline limestone. Sharply-developed, transparent, pale green crystals are frequently associated with adularia, asbestos and quartz in the crystal-lined crevices of the schists of the Swiss and Tyrolese Alps. Large, rough and dark-coloured crystals are found at Arendal and KragerS in Norway, and in granular limestone at Diana in New York and Eganville in Ontario. A greyish, compact and impure' variety of spheric, known as " leucoxene," frequently occurs in basic igneous rocks as an alteration product of ilmenite and rutile. (L. J. S.)
End of Article: SPHENE
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SPHAERISTERIUM (Gr. ackaipear 1pun)
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SPHENODON, or TUATARA

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