Diaspore is a native aluminium oxide hydroxide, a-AlO(OH), crystallizing in the orthorhombic system and isomorphous with goethite 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 colorless or greyish-white, yellowish, sometimes violet in color, and varies from translucent to transparent. It may be readily distinguished from other colorless transparent minerals with a perfect cleavage and pearly luster, like mica, talc, brucite, and gypsum by its greater hardness of 6.5 – 7. The specific gravity is 3.4. When heated before the blowpipe it decrepitates violently, breaking up into white pearly scales.
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 aluminium.
Diaspore along with gibbsite and boehmite are the major components of the aluminium ore bauxite.
Other names for diaspore include empholite, kayserite, tanatarite and spelling variations of these.