tjenth.] '■>^-' [August is, 



1. Corundum, altered into Spinel. 



a. At the Carter Mine, in Madison county, X. C, corundum is found 

 in white and pink crystals, but mostly in irregular grayish-white or white 

 cleavage masses, generally enveloping a variety of a delicate pink color. 

 Where small cracks or fissures occur in the corundum, it can be observed, 

 sometimes only bj^a small dark line, that a change has commenced Avhich 

 in many places extends through large masses, converting the corundum 

 into a massive greenish-black spinel, with uncA-en fracture, and of a fine 

 granular structure, rarely showing planes of octahedral crystals in the 

 compact mass. It yields a grayish-green powder and has a specific gravity 

 of 3.751. The spinel shows in manj^ cases small scales of prochlorite, into 

 which it finally passes. 



With difficulty I have selected some which was free from prochlorite, 

 but although the material appeared to be quite pure, it was found to con- 

 tain a small quantity of unaltered corundum = 1 .15%. The following 

 are the results of my analysis (a), and after deducting silicic acid and 

 corundum (b), calculated composition (c). 



a. b. c. 



6G.74 



1.34 



0.09 



0.33 



0.23 



11.94 



19.34 



100.32 100.00 100.00 



b. At the meeting of the American Philosophical Society of March 17, 

 1882, Dr. Edgar F. Smith and Mr. N. Wiley Thomas described corundum 

 from a locality, three-quarters of a mile north of Shimersville, in Lehigh 

 county, where numerous crystals had been ploughed up. I am indebted 

 to Dr. Smith for a variety of specimens. The crystals are mostly rough, 

 and show the hexagonal prism and pyramid and basal planes. Many of 

 them have some feldspar and mica attached, showing that they probably 

 come from a granitic gangue. The color of the crystals is generally gray, 

 a few, however, show a reddish or a pink color. Disseminated thi'ough 

 all the crystals and frequently accumulating on the surface, are minute, 

 very brilliant crystals of a highly titaniterous menaccanite ; these are not 



which he saddles on me, is Dr. Hunt's. I positively deny the possibility of such 

 a change in the following language: " Ido not know of a single inntancein winch 

 corundatn could have elii.iinated under such circumstances from the hydrate; on 

 the contrary, the presence of grains of corundum in the bauxite proves pretty con- 

 clusively that the latter results from the hydration of corundum, and that the 

 grains which have been found are remnants, not yet converted.'^ 



