1873.] d^J [Genth 



In the analysis of a, I found by the fusion with calcic carbonate and 

 amnionic chloride 21.40 per cent., and in b, 17.78 per cent, of free corun- 

 dum. 



The analysis of the reddish variety by C. W. Roepper contain? evidently 

 about 15 per cent, of corundum in the silicic acid which he found. 



S. P. Sharpless suggested that both varieties are the 'products of the 

 action, of water containing alkaline silicates upon corundum, and are more 

 nearly related to pinite than to any other mineral species ; Prof. Brush, 

 that both ephesite and lesleyite are mixtures of corundum, and probably 

 diaspore, with a mica, similar to the damourite found at the lesleyite locality ; 

 and that the foliated soft material is damourite or a hydrous mica near that 

 species. 



In my investigations I had already ascertained that lesleyite contains a 

 large per centage of free corundum, when I received the Appendix to 

 Dana's Mineralogy by Prof. Brush, and I am happy to be able to prove 

 that, at least, the greater part of his suggestions are correct. 



I do not believe that there is any admixture of diaspore, but calcula- 

 ting from the amount of potash found in the white lesleyite the per cent- 

 ages requisite for a damourite, most similar in appearance to it (see 

 analysis of damourite e by Dr. Koenij), we get : 

 SiO., = 



Al,6 3 = 



Xa.O = 



K,6 = 



H..0 = 



The analysis of Sharpless gives about 69 per cent, of damourite and 

 nearly the same amount of corundum as my own. 



The calculation of the analysis of the reddish variety gives less satis- 

 factory results, owing to the greater impurity of the mineral ; but it 

 corresponds with about 70 per cent, of damourite, 27 per cent, of corun- 

 dum and 3 per cent, of other admixtures. 



c. The third variety of lesleyite is of an entirely different nature. 

 The analysis gave : 



Sp. Gr. = 



SiO, = 



A1A 



Fe,0 3 



MgO 



LLO 



Na,0 



K 2 



Ignition 



Corundum 



100.13 99.55 



