Genth.] <J<b , rgep. 19i 



by Count Bournon, is the matrix of corundum in the Carnatic. Associ- 

 ated minerals are cyanite and garnet. It has been analyzed already by 

 Chenevix more than 70 years ago, and lately again by G. J. Brush* with 

 almost identical results, if we except the small quantity of soda which 

 the former had overlooked. Oxygen ratio of ROf : A1.,0 3 : Si0 2 = 1 : 

 3 : 4. 



b. A snow-white massive granular feldspar also occurs as the matrix 

 of corundum at Barsowskoi, near Kyschtimsk in the Ural, where G-. Rose 

 discovered it, who finding it different in composition gave it the name of 

 barsowite. Oxygen ratio of CaO : A1 2 3 : Si0 2 = 1:3:5. I have 

 seen only one specimen in which the grayish corundum in dipyramidal 

 crystals was disseminated through the feldspathic mineral. In fracturing 

 a piece the corundum crystals left a smooth impression upon the barsowite, 

 as if they were already hard when the latter was still in a plastic con- 

 dition. 



c. A snow-white or blueish-white cleavable variety of feldspar showing 

 a fine striation upon the cleavage planes, is found associated with a 

 greenish-black hornblende with a distinct cleavage angle of 124°, is 

 found at the Cullakenee corundum locality, but I have not been able to 

 detect corundum in any of the cleavable specimens, which I had for ex- 

 amination. See analysis below, (a). 



A granular and very compact variety with crystals of corundum dis- 

 seminated through it, is found at the same locality. In a fresh fracture 

 the corundum is hardly distinguishable, except by its somewhat grayer 

 color. In weathered specimens the corundum crystals, some of nearly 

 one inch in diameter, stand out in bold relief. They are very rough, as if 

 they were eaten, and in many of them a micaceous mineral, damourite 

 probably, is associated with them, which not only coats the outside but 

 penetrates even to the centre of the crystals. I received this variety too 

 late for chemical analysis. 



Together with massive gray corundum, partly altered into zoisite, is 

 rarely found at the same locality a white granular variety of feldspar, 

 much of the appearance of sugar, but pretty tough. It seems to have 

 been the result of the alteration of corundum. The analysis is given 

 below (b). 



d. Another fine-grained and very friable variety from Cullakenee has much 

 of the appearance of the oligoclase (indianite) of Chester, Massachusetts. 

 It is distinguished from the Chester mineral by a dissemination through 

 the whole mass of fine grains or crystals of hornblende, whilst the latter 

 contains biotite in their place. It has not been analyzed. 



I have already mentioned the triclinic feldspar, forming with smarag- 

 dite and red corundum, the peculiar rock which so nearly resembles that 

 from Hof in Bavaria. I have not been able to obtain it in a state of suffi- 

 cient purity for analysis. 



* Dana's Descriptive Mineralogy. 18'3S,339. 

 t RO = 1-y N a O J- 5-6 CaO . 



