146 A. F. BUDDINGTON 



increasing temperature for six days. The product obtained was a 

 zirconia-bearing pyrophyllite. Its specific gravity was 2.87 and 

 it appeared in thin hexagonal plates, which he states are not true 

 hexagonal plates unless there be optical anomalies. 



Le Chatelier (1887) determined the points at which pyrophyllite 

 loses its water by noting the points at which the temperature 

 remained constant with absorption of heat and found two such 

 points, the first at 700 and the second at 850 . 



From the foregoing data it is evident that pyrophyllite is a 

 mineral which may form under conditions varying from the high 

 temperatures of dynamic metamorphism to the near-surface tem- 

 peratures and pressures of solfataric agencies. 



TEMPERATURE OF FORMATION OF PINITE 



Pinite, if considered as an impure sericite, as suggested by 

 Clarke (191 1), has a varied range of conditions under which it may 

 form. Clarke states, however, that "the alteration [to sericite] is 

 most conspicuous in regions where dynamic metamorphism has 

 been most intense, high temperature, the chemical activity of 

 water and mechanical stress all working together to bring it 

 about." 



A green micaceous mineral described as mariposite by Silliman, 

 and whose composition, shown by two analyses, as suggested by 

 Hillebrand (1895), resembles pinite, is characteristic of the mother 

 lode in Tuolumne and Mariposa counties, California. 



Crosby (1880) describes pinite as a product of surface decom- 

 position of petrosilex and f el sites in the vicinity of Boston, Massa- 

 chusetts. Bell (1887) found it at Ballater Pass interspersed through 

 granitic rocks and along their joint planes, and ascribes its origin 

 to the decomposition or alteration of orthoclase feldspar, an inter- 

 mediate stage in its conversion into kaolin. 



