RE-EXAMINATION OF AMERICAN MINERALS. 121 



2. Orthoclase. — There is also associated with danburite a 

 potash feldspar not unlike the soda feldspar just mentioned ; in 

 some cases it is so intimately associated with it as to require 

 great care in selecting for analysis. So far as our observa- 

 tion extends, we have been able to identify the oligoclase by 

 its occurrence in masses with a broad cleavage surface, and 

 another less smooth, meeting at the angle 93°-94° ; in ortho- 

 clase this angle is 90°, and most frequently it presents at this 

 locality small cleavage faces, and is sometimes of a granular 

 structure. 



The following analyses are of the latter variety, which 

 doubtless contain a little oligoclase that it is impossible to 

 separate. 



1 2 



Silica 63.80 63.95 



Alumina 18.90 19.05 



Lime 80 .61 



Magnesia 20 .20 



Potash 11.43 10.95 



Soda 3.86 3.69 



Ignition 30 .50 



99.29 98.95 



The specimens examined were taken from the locality by 

 one of the authors. 



14. Haddam Albite, identical with Oligoclase. 



Associated with the iolite at Haddam, Conn., there occurs a 

 glassy feldspar which has heretofore been called albite. Its 

 composition is that of an oligoclase, as will be seen by the fol- 

 lowing analysis : 



1 2 



Silica 63.87 64.64 



Alumina 21.82 21.98 



Lime 2.14 2.17 



Magnesia trace trace 



Soda 10.18 9.80 



Potash 50 .50 



Ignition 29 .29 



98.80 99.38 



The specimens examined were received from Professor 

 Dana. 



We have examined the moonstone feldspar, from Mineral 

 Hill, Delaware County, Pa., which is also oligoclase. 



