RE-EXAMINATION OF AMERICAN MINERALS. 113 



The silica and peroxides* in these analyses are identical; 



but, in common with many of the micas, it is extremely difficult 



to deduce any one formula that would be a correct expression 



of their chemical constitution, owing to slight differences in 



the protoxides. This is rendered more obvious by comparing 



their oxygen ratios; 



£ & Si 



1. Litchfield mica 1:7.22: 9.70 



2. Liebnerite 1:6.33: 9.43 



3. Damourite 1: 9.35: 12.00 



4. Margarodite 1:6.16: 8.95 



The striking similarity of these species would lead us to 

 suspect that if new analyses were made of specimens from the 

 original localities, they might prove identical. In all physical 

 characters, except structure, there is a complete correspondence. 



4. TJNIONITE, IDENTICAL WITH OlIGOCLASE. 



This mineral was described by Prof. Silliman, jr., in the 

 Amer. Jour. Science and Arts, 2d series, viii, 384. The follow- 

 ing are its characters : In general appearance it resembles a 

 soda spodumene ; it has a very distinct cleavage in one direc- 

 tion; luster vitreous ; color white; hardness 6; specific gravity 

 2.61. It is found with euphyllite at the corundum locality 

 near Unionville, Pa. The results of three analyses are as 

 follows : 





Si 



£1 



IPe 



Ca 



Mg 



m 



K 



ign. 



1. 



64.09 



21.45 



trace 



0.86 



0.69 



10.94 



1.36 



1.02=100.41 



2. 



64.45 



20.97 



trace 



0.77 



0.46 



10.94 



1.36 



1.14=100.09 



3. 





21.70 



trace 



0.85 



0.49 







1.02 



The third analysis, owing to an accident, is incomplete; the 

 constituents determined are given for comparison. The oxygen 

 ratio of these analyses is very nearly 1:3:9, which gives the 

 formula &Si+£lSi 2 . This is the formula of oligoclase ; the 

 analyses correspond with that species, and the physical char- 

 acters being the same, there can be no doubt as to the identity 

 of unionite and oligoclase. 



It is believed that this is the first time that oligoclase has 

 been observed in the United States. 



* Considering the iron in Liebnerite as peroxide. 



