STUDIES IN HYDROTHERMAL ALTERATION 



195 



the same optical properties as these also appeared in experiment 

 No. 46 and are undoubtedly the same thing. 



The hornblende was unchanged in experiments No. 36 and 37; 

 the tube in No. 37 burst some time during the course of the heating. 



Group VII: Potassium bicarbonate solutions on feldspars and 

 hornblende.— These are similar to the experiments of Group VI, 

 except that potassium bicarbonate solutions were substituted for 

 the sodium bicarbonate solutions (Table VII). In no case either 



TABLE VII 



with the soda or potash feldspar or with hornblende did any change 

 appear in the minerals. The writer is unable to give an adequate 

 explanation of this fact, but it may have some bearing on the 

 question whether potash is introduced or not in hydrothermal 

 processes. 



Group VIII: Sodium tetraborate solution upon feldspars and 

 hornblende. — A few experiments were tried with borax solutions 

 with results very similar to those produced by the alkali carbonates 

 (Table VIII). In No. 43 well-formed crystals of analcite as rhom- 



TABLE VIII 



bic dodecahedra appeared. No alterations occurred in the other 

 experiments. 



Group IX: Sodium sulphide solutions upon feldspars and horn- 

 blende. — The presence of the metallic sulphides indicates that at 



