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 .