260 PHYSIOGRAPHY. CLASS n. 



what he calls Porcelain-spar, probably a variety of Labra- 

 dorite. 



2. Among several analyses referring to varieties of pris- 

 matic Feld-spar, and the allied species of Albite and Lab- 

 radorite, the following may serve for a comparison of their 

 chemical constitution. 



Prismatic Feld-spar. 



Adularia, analysed Labradorite from Common Felspar from 

 by Vauquelin. Norway, by Klaproth. Carlsbad, by Klaproth. 



64-50. 

 19-75. 

 11-50. 

 a trace. 



1-75. 



0-75. 



From Chesterfield in 

 Massachusetts bj Stromeyer. 



70-68. 

 19-80. 



9-06. 



0-23. 

 Oxide of Iron 

 and Manganese 0-00. 0-00. I'll. 



Ldbradorite. 



From Labrador by From Siebenlehn near Porcelain-spar from 

 Klaproth. Freiberg by Klaproth. Passau by Fuchs. 



Silica 55-75. 51-00. 49-30. 



Alumina 26-50. 30-50. 27'90. 



Lime 11-00. 11-25. 14-42. 



Soda 4-00. 4-00. 5-46. 



Oxide of Iron 1-25. 1*75. 0-00. 



Water 0-50. 1-25. 0-90. 



The formulae of the composition of these three species, 

 according to the method of BERZELIUS, are K S 3 + 3 A S* 



