54 M. Rose on Felspar, [Jan. 



Silex. 68-84 



Alumina, with a little oxide of iron and 



lime 20-53 



Soda 9-12 



98-49 



If the composition of albite is calculated from the formula 

 NS 5 + 3 A S 3 , the following proportion of the constituent 

 parts is found 



Silex 69-78 



Alumina 18-79 



Soda 11-43 



Crystallized albite is found at Arendal in Norway, where it is 

 almost always accompanied with epidote, according to what I 

 have seen at the place itself, as well as in private collections. It 

 is found also in the Schmirnerthal, in the Tyrol, with carbonate 

 of lime in veins of carbonate of lime; at Rohrberg, near 

 Zell, in veins with quartz, or in gneiss very rich in quartz, 

 accompanied by rock crystal and carbonate of iron : it is found 

 in the same circumstances at Gastein, in the country of Salz- 

 bourg ; at Bareges in the Pyrenees, and at Auris in Dauphiny, 

 in veins with axinite, anatase, adularia, epidote, asbestus, 

 with which the albite is sometimes perfectly mixed. As to 

 the albite of Kerabinsk, in Siberia, the collection of minerals 

 in the University of Berlin, contains only isolated hemitrope 

 crystals, which are of a much larger size than the others. Some- 

 times the plane M is one inch long, while the other hemitrope 

 crystals are never more than a few lines. At Prudelberg, at 

 Stonsdorf, near Hirschberg, in Silesia, albite is found with fel- 

 spar in veins of granite ; the crystals of felspar are flesh-co- 

 loured, and sometimes covered with crystals perfectly white, or 

 of the same colour as those of albite. The crystals of felspar of 

 Baveno are also frequently accompanied by some small whitish 

 crystals, which commonly are not felspar, but albite.* 



Observations. — The crystals of albite are easily distinguished 

 by their hemitropes, and the re-entering angles formed by the 

 planes P. If the crystals of felspar were grouped in the same 

 way, the similar planes of the two crystals would be parallel, 

 since in felspar the planes M and P are at right angle to each 

 other, and could never form re-entering angles ; the analogous 

 hemitrope crystals of felspar, such as those of Carlsbad, can 

 only be formed as it has been demonstrated by M. Weiss, when 

 two crystals are grouped, either with their right planes M, or 

 with their left planes M. So that the faces P of cleavage are 

 situated on opposite sides in the two crystals, while in albite 

 the planes P of the two crystals are situated on the same side. 



* If the abovt-mentioned crystals of St. Gothard are albite. 



