1873.] 



377 



[Genth. 



From this locality I have the analyses of the cleavable snow-white va- 

 riety (a) by Dr. Koenig ; and of the fine-grained, like sugar, probably re- 

 sulting from the alteration of corundum, by Mr. Thos. M. Chatard (b) 

 They found : 



Sp. Gr. 



SiO, 



ALA 



FeA 



MgO 



CaO 



Na_,0 



K.fi 



Ignition 



12.42 



4.09 



12.19 



3.74 



100.48 100.20 



The oxygen ratios in the two analyses are as follows : 

 RO : RA = SiO, in « — 4.09 : 12.42 : 30.55 = 0.99 : 3 : 7.51 

 in b = 3.74 : 12.19 : 31.15 = 0.93 : 3 : 7.07 

 which is near the atomic ratio of 1 : 1 : 4, agreeing with the formula 

 of andesite = (Na 2 0, CaO) Si0 2 + ALA, 3Si0 2 . 



e. The soda-oligoclase, which, associated with euphyllite, accompanies 

 corundum at Unionville, Pennsylvania, has been analyzed by Smith and 

 Brush*. 



A specimen in the University collection from the same locality consists 

 of a granular yellowish or brownish-white oligoclase, the small cleavage 

 planes of which are sometimes finely striated. It has patches of a 

 granular gray corundum disseminated through the mass, mixed with 

 minute grains of a hard greenish-black mineral, pi-obably spinel. The 

 corundum in some places altered into a soft crypto-crystallme slightly 

 pearly, white or grayish-white mineral, which appears to be margarite ; 

 it is frequently penetrated by the oligoclase and looks as if it was a rem- 

 nant from its conversion into oligoclase and other species. The analysis 

 of it by Mr. Chatard gave : 



contains oxygen 



31.65 

 11.26 



0.18 

 0.14 

 0.88 

 1.86 

 0.64 



11.44 



100.50 

 The oxygen ratio of RO : R 2 0, : SiO, = 3.52 



* Sill. Joura. [2] XV, 211 and XVI, 44. 

 A. P. S. — VOL. XIII.— 2V 



11.44 : 31.65 



