EUCLASE  , a very rare

mineral, occasionally cut as a gem-stone for the cabinet . It bears some relation to beryl in that it is a silicate containing beryllium and aluminium, but hydrogen is also present, and the analyses of euclase lead to the formula HBeAlSiOs or Be(AlOH)SiO4 . It crystallizes in the monoclinic system, the crystals being generally of prismatic habit, striated vertically, and terminated by acute pyramids . Cleavage is perfect, parallel to the clinopinacoid, and this suggested to R . J . Hauy the name euclase, from the Greek et), easily, and icXliais, fracture . The ready cleavage renders the stone fragile with a tendency to chip, and thus detracts from its use for personal ornament . The colour is generally pale-blue or green, though sometimes the mineral is colourless . When cut it resembles certain kinds of beryl (aquamarine) and topaz, from which it may be distinguished by its specific gravity (3.1) . Its hardness (7.5) is rather less than that of topaz . Euclase occurs with topaz at Boa Vista, near Ouro Preto (Villa Rica) in the province of Minas Geraes, Brazil . It is found also with topaz and chrysoberyl in the gold-bearing gravels of the R .

Sanarka in the

South Urals; and is met with as a rarity in the mica-schist of the Rauris in the Austrian Alps .