Q7^> 



Genth.] " < « LSep. 19, 



The spinels from Unionville, Pennsylvania, and Dudleyville, Alabama, 

 contain only traces of chromic oxide and are probably mixtures of pleo- 

 naste and hercynite. 



3. Diaspore. 



Diaspore has been observed in many places as the result of the hydra- 

 tion of corundum, but I am not aware that ever a real pseudomorph has 

 been met with. 



J. L. Smith (loc. cit.) has made the very important observation that all 

 the corundum, wliich he had examined, contained water in variable 

 quantities from 0.68 to 3.74 per cent., but states that the more careful 

 and repeated examination showed the absence of diaspore or any other 

 hydrate of alumina. May it not be that the diaspore is so very minutely 

 distributed through the corundum, that even the best microscopic, or 

 other examination could not detect it, as I just have shown with regard 

 to the admixture of corundum in spinel? — On page 58 he makes the 

 following remark : " Yet of all the specimens collected, none offer so 

 " much interest as those of diaspore imbedded in the corundum ; here we 

 "see the two minerals, without being able, in many places to distinguish the 

 u line of separation, so imperceptible is the gradation. After what has 

 " been said in respect to corundum, it is not astonishing to see this con- 

 ll, neetion of alumina more or less hydrated, with a hydrate of alumina of 

 " definite composition.'''' 



The diaspore from the different localities has been so fully described 

 that I have but little to add. 



"With the exception of the locality of Chester, Mass., where it had been 

 found in considerable quantity and of great beauty, diaspore is a rare 

 mineral in this country. Most beautiful crystals of it were found at the 

 Unionville, Pa. locality, by Dr. Isaac Lea,* who gave a description of them 

 before the Academy of Natural Science. 



J. C. Trautwinef first noticed this mineral in cavities of the massive 

 corundum from the Culsagee Mine, North Carolina, where it occurs in 

 very minute but beautiful acicular crystals of the usual forms. Only 

 one or two specimens have thus far been discovered. 



I have not been able to detect it at any other of the North Carolina, 

 South Carolina, Oeorgia or Alabama corundum localities. 



4. Beauxite. 



This hydrate of alumina, generally mixed with a considerable quantity 

 of ferric hydrate and a hydrous aluminous silicate, occurs in consider- 

 able quantities in the southern part of France ; it incloses occasionally 

 grains of corundum. 



T. S. Hunt's:): remarks about this interesting fact, are as follows : 

 " By intense heat this substance (beauxite) is converted into crystalline 



♦Proceedings of the Academy Natural Sciences, April 9, 18S7. 

 tJourn. Franklin Institute, XCIV. 7, 

 tT. S. Hunt, Sill. Journ. [2] xxxii. 2S8. 



