PAIGE AND STEIGER: SERICITIZATION 



235 



altered to kaolin, and here again where fractures are plentiful 

 and the descending solutions have been active, considerable parts 

 of the rock in the aggregate have been altered to this mineral or a 

 closely allied compound. 



The formation of sericite from feldspar is usually assigned to the 

 action of either heated water alone or to the action of heated 

 water containing carbonate. As may be observed at many places, 



Fig. 1. Illustrating the replacement of breccia by veins of kaolin without 

 movement along the veins. 



sericite forms with ease from oligoclase, orthoclase, andesine, 

 and labradorite. According to Lindgren,- this fact was first 

 described by Bischof,^ who also furnished the chemical explana- 

 tion. The potassium carbonate contained in the water changes 

 the sodium-bearing silicate into potassium silicate, which unites 

 with the aluminum silicate to form sericite. 



In the copper deposits at Tyrone, New Mexico — deposits that 

 are typical chalcocite deposits resulting ''from secondary enrich- 



- Lindgren, Waldemar, Meiasomatic processes in fissure veins. 

 Inst. Min. Eng. 30: 31-608. 1901. 



= BiscHOF, Chemische Geologie, I, p. 31 et seq; also p. 44. 



Trans. Amer. 



