204 Mineralogy of Southern India. 



was doubted if the copper had not been taken up from 

 the silver crucible, which might not be quite pure. The 

 analysis contained no lime. The following is a tolerable 

 approximation to the composition: — 



Silica, .. .. .. 40.11 (and Titanic acid ?) 



Magnesia, 39.15 



Iron, (peroxide,) . . . . 6.84 



Alumina, . . . . . . 0.53 



Copper, (oxide,) .. .. 0.50? 



Water, .. .. .. 13.50 volatilized by heat. 



100.63 



The iron was supposed to be in the state of peroxide, as 

 yellow ochres, &c. are thus coloured. No reliance can of 

 course be placed on the quantity of water, as the mineral 

 was hygrometric, but the other numbers have been computed 

 from the weight of the ignited analysis. 



Naggery black Pot-stone. 



This is another magnesian mineral, from the Naggery 

 hills, north-west of Madras, given to me by Mr. Fisher of 

 Salem. It is cut into snuff-boxes, &c. by the natives of the 

 place. I have no account of its geological associations. Cha- 

 racters are — Colour : lead coloured black, much the same as 

 black granite : Structure, imperfectly granular, and homoge- 

 neous : fracture, imperfectly conchoidal ; imperfectly granular 

 to lens : appears a little speckled. Lustre magnesian, and 

 bluish. Streaks bluish white. Smell : sulphurous. Spec. grav. 

 much less than black granite. Tough, and with difficulty 

 broken: hardness but little more than steatite, or pot-stone: 

 feels rough, but perceptibly greasy. I do not find that I have 

 attempted to analyse it. 



Binary Granite. 



A granular aggregation of white quartz, and resplendent 

 or glistening felspar. The crystals of each mineral being 

 each perfectly formed, and totally distinct, so as to be easily 



