CORUNDUM, in mineralogy. Though corundum appears to have been known to Dr. Woodward, it may be said to have been first distinguished from other mine rals by Dr. Black. In 1768, Mr. Berry, al'apidary in Edinburgh, received a box of it from Dr. Anderson of Madras. Dr. Black ascertained that these specimens differed from all the stones known to Eu ropeans ; and, in consequence of its hard.. ness, it obtained the name of adamantine spar. It is found in Hindostan, not far from the river Cavery, which is south of Madras, in a rocky matrix of considera ble hardness, partaking of the nature 'of the stone itself. It occurs also in China, and in Ceylon, Ava, &c. The Count de Bournon pointed out the resemblance be tween this mineral and the sapphire, in a dissertation published by him and Mr. Creville in the Philosophical Transac tions for 1798, and suggested it as proba ble, that corundum may be only a variety of the sapphire ; and that the seeming difference in their ingredients is owing to the impurity of those specimens of corun dum, which have hitherto been brought to Europe. This conjecture has been since
confirmed by a subsequent dissertation of Bournon, and the chemical analysis of Chenevix. Werner subdivides it into two species, namely, corundum, and adaman tine spar ; but, in reality, they seem to be only varieties, or, at most, subspecies of the same species.' The chief difference exists in the colours.
Corundum has been found in India, in the carnatic, and on the coast of Malabar. It occurs massive, in rolled pieces, and crystallized ; crystals the same as in sap , phire ; colour greenish-white, passing in to greenish-grey, and asparagus-green, sometimes pearl grey, which passes into flesh-red; surface rough ; fracture foli ated ; specific gravity 3.7 to 4.2.
Mr. Chenevix obtained the following constituents from the specimens of the enrunclums, which he subjected to chemi cal analysis.