44 Chemical Examination of American Minerals. 



sible, still very small fragments of quartz would occasionally 

 adhere to them. If we make allowance for this excess, we 

 may consider nacrite as a bisilicate of alumina. It obviously 

 constitutes a peculiar species. 



Vauquelin, in an analysis of nacrite, detected in it 17'5 per 

 cent, of potash. But the American variety contains no 

 potash, or only a minute quantity, since I did not succeed in 

 detecting any in it. 



Note. There appears to be some confusion in the books re- 

 specting nacrite. The green mineral of Maine, differs in some 

 of its characters, from the description of nacrite in Phillips, and 

 Cleaveland, for it fuses with difficulty, and possesses scarce- 

 ly any unctuous feel. The European mineral appears to 

 have been twice analyzed by Vauquelin, for its composition, 

 as stated by Cleaveland, differs very materially from the 

 analysis quoted by Dr. Thomson. In the former case, the 

 quantity of potassa is said to be 1 7*5, in the latter 8. Dr. 

 Thomson found no alkali. 



13. XANTHITE. 



I have given this name to a mineral which I got about a 

 year ago from Mr. Nuttall : it was found at Amity, Orange 

 County, New-York. The specimen in which the xanthite 

 occurs, is a rock composed of three distinct substances in 

 grains. 



1. Calcareous spar. 



2. Xanthite. 



3. Dark-green opaque grains. 



The xanthite constitutes by far the greater part of the 

 stone. It has a light grayish-yellow color, and consists of a 

 congeries of very small rounded grains, easily separable from 

 each other, and not larger than small grains of s?ind. 



