Cyanite

Cyanite, KYANITE (Gr. kyanos, 'blue'), DISTHENE, or SAPPARE, a mineral composed of alumina and silica. It often occurs crystallised, and generally in broad prisms. It is sometimes colourless, red, yellow, &c., but more frequently of a fine sky-blue, slightly tinged with violet; it is transparent, and sometimes beautifully opalescent.