LESLEYITE OF CHESTER COUNTY, PENN. 181 



Heated before the blowpipe, it becomes milk-white but does not fuse. At 

 first sight it might be taken for white disthene. It is decomposed with great 

 difficulty by carbonate of soda, even with the addition of a little caustic soda." 

 The lesleyite has identically the same properties. On an- 

 alysis the two minerals were found to be composed as follows : 



Ephesite. Lesleyite. 



Silica 30.70 31.18 



Alumina 55.67 55.00 



Lime 2.55 .45 



Soda 5.52 1.20 



Potash 1.10 7.28 



Water 4.91 4.80 



100.45 99.91 



The alkalies in the two varieties are reversed, the Ephesite 



containing principally soda and the Lesleyite potash. 



This close relation of the two minerals is an interesting fact 



as regards the associate minerals of corundum found in different 



parts of the world. 



In regard to the reddish variety of Lesleyite examined by 



Eoepper, the analysis can not be considered as giving very 



satisfactory results, for the mineral may have been impure, and 



the difficulty in decomposing by the soda fusion may give very 



erroneous results in a silica determination. 



13 



