Art. XXV.—Mineral Resources of Southern India. No. 7. Corundum, Ruby, and Garnet Localities

Extract

Comparative Remarks on the Geognostic Position of the Corundum in Europe and India.—As I am not aware of any detailed account having been published regarding the geognostic position of the corundum in Peninsular India, and since the rocks with which it is associated in the particular locality which I first visited differ from those in which it has been stated to occur in Europe and Southern India, I am induced to preface this paper with the following remarks. Professor Thomson (Outlines of Mineralogy, vol. i., p. 213) informs us that “the corundum occurs in imbedded crystals in a rock which consists, according to Count Bournon, of indianite, and contains felspar, fibrolite, several varieties of augite, and also octohedral iron ore; the hair-brown or reddish-brown varieties are called adamantine spar. They occur with fibrolite and octohedral iron ore in a sort of granite containing no quartz.” And again (p. 256) he states, that “fibrolite is a mineral found accompanying crystals of corundum in the Carnatic, and that it is a component part of the granite, which is the matrix of the corundum of China.” Professor Jameson, in his geognosy of Peninsular India,(Ed.Cab.Lib., No.VIII., p.349–50,) gives a summary of what is known regarding the corundum of Southern India, and states that it occurs embedded in granite and sienite in the district of Salem, in the Madras Presidency, among the mountains of the Carnatic, and in other parts of the Peninsula, associated with cleavelandite, indianite, and fibrolite. Now in the locality I am about to describe, it was found to occur in decomposed beds of a talcose slate, to which gneiss is subordinate, associated with nodules of indurated talc, and of a poor quartzy iron ore: asbestus, chlorite, actinolite, and schorl were found embedded in the talcose slate.