134 A. F. BUDDINGTON 



The pyrophyllite may occur either as single well-defined veins, 

 or as a series of veins, pockets, and lenticels, which together con- 

 stitute what may be called a pyrophyllitic zone. 



The former character is illustrated at talc prospect 5, where the 

 pyrophyllite forms a vein about 500 feet long and varying from 6 

 to 15 feet in width in a white, densely spherulitic rhyolite. Near 

 the one end of the vein which is exposed the pyrophyllite is full 

 of nodules and stringers of the rhyolite, but becomes almost clear 

 pyrophyllite in its central portion. 



The latter character (pyrophyllitic zone) may be illustrated by 

 the character of the pyrophyllite deposits at talc prospects 1 and 2. 

 The country rock of the pyrophyllitic zones may be so altered as 

 to constitute a quartz-pyrophyllite schist consisting of micro- 

 crystalline quartz and pyrophyllite, as at talc prospect 1, or it may 

 be partially pyrophyllitized, as at talc prospect 2, or relatively 

 unaltered as at talc prospect 4. 



At talc prospect 1 large masses of pyrophyllite occur in pockets 

 from 1 to 1 5 feet in diameter containing more or less country rock, 

 or as thin sheets incasing lenses of quartz-pyrophyllite rock oriented 

 parallel to the cleavage. It frequently occurs as an interlacing 

 network of films veneering lenses of the quartz-pyrophyllite rock 

 or as lenticels replacing the matrix between adjacent quartzose 

 nodules. The pyrophyllite (222 E 2 f x) usually serves simply 

 as a matrix for these nodules varying from a fraction of an inch to 

 several feet in diameter, and even hand specimens are infrequent 

 which do not contain one or more of them. Ramifying stringers 

 of country rock may wander aimlessly through the pyrophyllite 

 (Fig. 3) and veins of pyrophyllite reticulate in the country rock. 

 It is quite possible that the nodular structure originated through 

 the total replacement by pyrophyllite of the sheared zones between 

 lenses of a rhyolite like that shown in Fig. 2, and the alteration 

 of the lenses themselves to a quartz-pyrophyllite rock. On the 

 west side of the talc mine here small pockets of cream-colored 

 pyrophyllite, weathering green or yellow, are found replacing the 

 matrix of a very coarse rhyolite breccia. 



At talc prospect 2 there is a pyrophyllite zone about 30 feet 

 wide in which pyrophyllite constitutes from a small percentage 



