Genth.j 400 [Sep. 19, 



With a strong magnifying glass it is shown to be crystalline, and to con- 

 sist of exceedingly minute scales with a pearly lustre, radiating from a 

 nucleus of gray corundum, which occupies the centre of the crystal, so 

 that the cryptocrystalline mineral has a somewhat fibrous (pseudofibrous) 

 structure. On the outside of the mineral are small scales of damourite. 

 I have made two analyses of the purest cryptocrystalline mineral, which 

 closely corresponded, and of which I give below the mean result (al.) 

 For corroboration, I have made a third analysis of material, which was 

 not as pure and contained a few scales of the damourite, the influence of 

 which upon the analysis («2.) will be noticed by the increased amounts 

 of silicic acid and potash and a reduction in the quantity of lime. 



b. A laminated white variety, having a very faint reddish tint, occurs 

 rarely with the granular corundum recently discovered. It it associated 

 with black tourmaline and forms a coating upon or small veins in the 

 grayish-white corundum. The laminae are sometimes nearly one inch 

 broad, but usually smaller. My analysis is given below (5.) 



c. An aggregation of fine scales and laminae somewhat of a granular 

 structure, also of a white color with a faint reddish hue, and associated 

 with black tourmaline, appeared to be a mixture of margarite with 

 corundum ; on powdering, however, it was found to be almost free from 

 the original mineral, which existed in it only in very minute grains. 

 The carefully selected material was analyzed by Dr. G. A. Koenig (c). 



d. A massive apparently compact or finely granular variety, has lately 

 been found with the granular corundum ; strongly magnified it appears 

 as an aggregate of very small scales ; on one side they are bounded by an 

 aggregate of larger scales, intermixed with chlorite. Its. color is white, 

 but there are many ferruginous brownish-yellow spots disseminated 

 through the mass. The purest which could be selected was analyzed by 

 myself (d). 



e. A compact variety, frequently containing fragments of unaltered 

 corundum, has been analyzed by Mr. Thos. M. Chatard (<?). It has a 

 grayish-white to brownish-white color, and breaks easily into angular 

 fragments of one or two inches in size, which are generally coated with 

 hydrated ferric and manganic oxides. The margarite itself shows under 

 the microscope a cryptocrystalline structure, it has a slight waxy lustre. 



/. The margarite, which was found associated with the boulder of blue 

 corundum, near the French Broad Biver, Madison County (formerly 

 Buncombe County), North Carolina, has been analyzed by B. Silliman 

 (1. a). 



g. At the Culsagee Mine, North Carolina, margarite is a rare mineral. 

 I have noticed it only in a rock, consisting of a feldspathic mineral, 

 mostly decomposed into kaolinite, a greenish hornblende, and small 

 quantities of a chloritic mineral, the whole mass intermixed with white 

 and pink corundum and laminae of margarite. (I have not mentioned 

 this rock above, because its occurrence seems to be local and I have no 

 further information about it). 



