CHRYSOBERYL  , a yellow or

green gem-stone, remarkable for its hardness, being exceeded in this respect only by the diamond and corundum . The name suggests that it was formerly regarded as a golden variety of beryl; and it is notable that though differing widely from beryl it yet bears some relationship to it inasmuch as it contains the element beryllium . In chrysoberyl, however, the beryllium exists as an aluminate, having the formula BeAl2O4, or BeO•Al2O3 . The analysis of a specimen of Brazilian chrysoberyl gave alumina 78•Io, beryllia 17.94, and ferric oxide 4.88% . The typical yellow colour of the stone inclines in many cases to pale green, occasionally passing into shades of dark green and brown . The iron usually present in the mineral seems responsible for the green colour . Chrysoberyl is often mistaken by its colour for chrysolite (q.v.), and has indeed been termed Oriental chrysolite . In its crystalline forms it bears some relationship to chrysolite, both crystallizing in the orthorhombic system, but it is a much harder and a denser mineral . As the two stones are apt to be confounded, it may be convenient to contrast their chief characters: Chrysoberyl . Chrysolite . Hardness . . .

8.5 6.5 to 7 Specific Gravity . 3.65 to 3.75 3.34 to 3.37 Chemical

Composition . . BeAl2Oa . Mg2SiO4 . Chrysoberyl is not infrequently cloudy, opalescent and chatoyant, and is then known as " cymophane " (Gr. agaa, a " cloud ") . The cloudiness is referable to the presence of multitudes of microscopic cavities . Some of the cymophane, when cut with a convex surface, forms the most valuable kind of cat's-eye (see CAT'S-EYE) . A remarkable dichroic variety of chrysoberyl is known as alexandrite (q.v.) . Most chrysoberyl comes from Brazil, chiefly from the district of Minas Novas in the state of Minas Geraes, where it occurs as small water-worn pebbles . The cymophane is mostly from the gem-gravels of Ceylon . Chrysoberyl is known as a constituent of certain kinds of granite, pegmatite and gneiss . In the United States it occurs at Haddam, Conn.; Greenfield Centre, near Saratoga Springs, N.Y.; and in Manhattan island .

It is known also in the

province of Quebec, Canada, and has been found near Gwelo in Rhodesia . (F . W .