486 On a Granular Albite associated with Corundum. 



but associated with corundum, which occurs implanted in it. 

 This analysis was made by Mr. M. C. Weld. Quantity 

 taken,2-180 grms. Found — 



2-1860 100-272 



This obviously yields the same formula as the last analysis. 



The extreme hardness of this mineral is its most remarkable 

 quality, and is not easily accounted for. It is probably con- 

 nected with its association with corundum, for we find the 

 quality equally developed in the Indianite (or anorthite), the 

 Asiatic associate of the same species. 



Analysis of Indianite. — I thought it of interest, in connexion 

 with the foregoing analyses, to make a new analysis of Bour- 

 non's Indianite, which, as already remarked, is found to be 

 the matrix of the corundum in India. Being possessed of an 

 authentic specimen, I requested Mr. Brush to conduct the 

 analysis, the results of which are now given. This mineral is 

 granular, and of a pink colour, sometimes gray or blackish; 

 very tough and hard. Hardness, 7 to 7-25. Gravity, 2-668. 

 It gelatinized completely in cold hydrochloric acid. Before 

 the blowpipe alone, infusible. The analysis gave on 1-594 

 grm.— 



Silica . . . 

 Alumina and a 

 trace of iron 

 Lime . . . 

 Soda . . 



1-6077 100-84 

 4Si08, R2 0% sR0 = 3R0, Si03 + 3(R2 O^ SiO^), 

 which is the formula for anorthite. 



