STUDIES IN HYDROTHERMAL ALTERATION 



197 



compounds richer in alumina to be exceeded, a few experiments 

 with aluminate solutions were tried. These solutions were pre- 

 pared by taking a weighed quantity of aluminum sulphate, precipi- 

 tating the aluminum as hydroxide, washing the precipitate and then 

 adding it to normal sodium or potassium hydroxide and diluting 



one-half. After this had been allowed to stand for several hours it 

 was filtered from its slight precipitate (Table X). In No. 49 anal- 

 cite crystals formed, which were identified chemically and micro- 

 scopically. In Nos. 50, 51, and 52 twinned 

 hexagonal plates, with anomalous division into 

 fields under polarized light, resulted, as shown 

 in Fig. 8. These gelatinize with hydrochloric 

 acid and contain sodium, but no aluminum could 

 be detected in them by a microchemical test. 

 The hornblende was not attacked. 



Group XI. — Albite and hornblende 



heated for 15 days at 280 C, with saturated J* from ex P eriments 



. Nos. 50, 51, and 52. 



solutions of calcium bicarbonate. The tubes 



burst in each case and the minerals showed no change. 



Fig. 8— Twinned 

 Were hexagonal plate result- 



GEOLOGIC BEARING 



Though the alteration of feldspars to analcite has not been com- 

 monly described, in many cases it is very possible that some of the 



