DIASPORE  , a native

aluminium hydroxide, AlO(OH), crystallizing in the orthorhombic system and isomorphous with gothite and manganite . It occurs sometimes as flattened crystals, but usually as lamellar or scaly masses, the flattened surface being a direction of perfect cleavage on which the lustre is markedly pearly in character . It is colourless or greyish-white, yellowish, sometimes violet in colour, and varies from translucent to transparent . It may be readily distinguished from other colour-less transparent minerals, with a perfect cleavage and pearly lustre—mica, talc, brucite, gypsum—by its greater hardness of 62-7 . The specific gravity is 3.4 . When heated before the blowpipe it decrepitates violently, breaking up into white pearly scales; it was because of this property that the mineral was named diaspore by R . J . Hairy in 18or, from Stavreipew, " to scatter." The mineral occurs as an alteration product of corundum or emery, and is found in granular limestone and other crystalline rocks . Well-developed crystals are found in the emery deposits of the Urals and at Chester, Massachusetts, and in kaolin at Schemnitz in Hungary . If obtainable in large quantity it would be of economic importance as a source of alumina . (L . J .