1882.] ^^'^ rOenth. 



b. At the Hogback Mine, Jackson county, N. C. , most of the corundum 

 which is altered changes into muscovite, but margarite also occurs. It is 

 found with corundum, associated with an earthy yellowish mineral, like 

 that of Gainesville, Ga., mentioned in my first paper, in which it is im- 

 bedded in small white pearly scales, often fan-shaped and radiating from 

 a center. I had only a small quantity of not cjuite pure material, of which 

 I have made a partial analysis (b). 



c. I have analyzed a specimen from Unionville, Pa., which is quite 

 interesting : — 



The mass consists of a greenisli-white, compact mineral, showing only 

 very slightly a fine granular structure. luterlaminated are very thin 

 micaceous strata, separating the compact mineral into layers ; the whole 

 inclosing a nucleus of unaltered gray corundum. The outside of the mass 

 is coated with a scaly mica, the individual scales varying from 1 to 2""" in 

 size, which is evidently the result of an alteration, showing in the first 

 place the change of corundum into compact margarite, and secondly, the 

 change of the latter into muscovite. 



The analysis of the margarite, as pure as can be selected, is given below 

 (c 1), but also a partial analysis of the resulting muscovite, but of material, 

 containing an admixture of margarite (c 2). 



d. Very remarkable specimens of corundum, usually surrounded by 

 margarite have been found at Ilendrick's farm, Iredell county, N. C. The 

 corundum occurs in hexagonal crystals, sometimes tapering, as if they 

 were very acute hexagonal pyramids, with basal plane. They are very 

 perfect and from 50 to 125""" in length, of a pale brownish or grayish- 

 white color. Many of the specimens contain numerous cavities which in 

 most cases are small and indistinct, so that it is difficult, if not impossible, 

 to suggest, what may have produced them, others show a hexagonal form, 

 but in one specimen, which contains larger cavities, some from 10 to 15""° 

 in size, very little doubt is left that the mineral which previously occu- 

 pied them vyas corundum in crystals showing a hexagonal pyramid and 

 prism. 



The corundum from Hendrick's farm is always altered on the surface, 

 which is enveloped " by a coating of margarite, from 1 to 6"™ in thick- 

 ness. It is rarely subfibrous and fine scaly, but mostly compact and more 

 or less porous. It has some black tourmaline in small crystals or crystal- 

 line groups imbedded in it, and on its surface it is beginning to change 

 into muscovite. Where the margarite is in contact with the corundum, 

 the latter has become rough and eaten. The analysis of the purest from 

 this locality gave me the results (d 1), a less pure specimen was analyzed 

 in the Laboratory of the University of Pennsylvania by Mr. Prank 

 Julian (d 2). 



