1373.] 401 [Gcntb. 



The pure margarite is white and has a pearly lustre. It has been 

 analyzed by myself (gl) and Mr. Chatard (g2). 



h. The most beautiful varieties of margarite occur at the Cullakenee 

 Mine, Xorth Carolina. Here it occurs in groups of laminated crystals, 

 distinctly showing the lateral planes of the same. The largest group, 

 which I have seen is two inches long, one and a-half wide and five- 

 eighths inches thick. The color of the basal cleavage planes is brownish- 

 white, but after treatment with dilute chlorhydric acid, which removes a 

 thin coating of ferric hydrate, the color is slightly pinkish-white with a 

 hue of silver-gray ; the lateral plaues have a darker color. 



Tourmaline is sometimes inclosed between the laminae, and they are 

 in some of the specimens intersected by crystals of an unknown mineral, 

 to which I have already alluded. The most important association, 

 however, are the nuclei of corundum, completely invested by the groups 

 of laminated margarite. There are also scales of a bronze or brownish- 

 yellow mineral, "probably the result of the alteration of margarite, which 

 I shall describe farther on as dudleyite. Mr. T. M. Chatard has analyzed 

 this variety {hi). 



Another from the same locality occurs as the product of the change of 

 grayish-white corundum. It is frequently associated with zoisite, and 

 intermixed with corundum in the form of broad laminae of a delicate 

 pink color. I have made an analysis of it (see 7i2 below). 



Associated with the mineral which I described as willcoxite, rarely oc- 

 curs a somewhat fibrous variety made up of microscopic scales of marga- 

 rite of a pearly lustre. It resembles much the variety of damourite e, 

 but was found by qualitative analysis to be margarite, containing a 

 considerable quantity of lime, but no potash. It completely surrounds 

 a mass of gray corundum. 



Still another variety from the Cullakenee Mine is found in thin seams 

 of a grayish-green color. When magnified, the mineral consists of an 

 aggregate of minute pearly scales of a greenish-white and sea-green color. 

 I give the analysis, which I made under A3. 



i. Crystalline masses of gray corundum from near Penland's, Clay 

 County, North Carolina, which I have examined, are coated with a 

 cryptocrystalline pseudofibrous mineral of a white and yellowish-white 

 color, which gave by qualitative analysis, a considerable quantity of 

 lime, but no potash, and which therefore appears to be margarite. 



A similar coating containing lime, is sometimes found on the blue 

 crystals of corundum from Crowder's Mountain, Gaston County, North 

 Carolina. 



These coatings on corundum crystals, which have been observed 

 frequently, are sometimes not thicker than a thick varnish, sometimes 

 the whole crystal has been altered, leaving not even a core oi the original 

 mineral. 



k. I have above alluded to the kidney-shaped and irregular masses 

 from Gainesville, Hall County, Gaorgia, which consist of a nucleus of 

 a. p. s. — VOL. XIII. 2y 



