G. F. Becker — Metamorphic rooks of California. 355 



seen in the field, the transformation begins along the cracks, 

 working toward the centers of the included fragments. 

 Where the process is incomplete the structure produced is 

 entirely analogous to that of decomposing olivines as seen 

 under the microscope. Sometimes, but not often, the serpen- 

 tine assumes a radial form, the fibers being normal to the 

 surface of the nucleus. Prof. Whitney observed such a case at 

 New Idria, and I found a very beautiful one at Knoxville. 

 The serpentinoid rocks usually show evidence of very violent 

 dynamical action. 



Under the microscope it can be shown, as I think, beyond a 

 question, that all of the principal components of the sandstones 

 and granular metamorphic rocks are subject to serpentinization. 

 After the investigations of von Drasche, Hussak, Bichstadt, 

 Weigand and others, it will surprise no one to learn that 

 augite and hornblende are converted to serpentine.* The 

 decomposition begins along the surfaces and cracks exactly as 

 in the case of chloritization and uralitization. Though vom 

 Eath, Bischof and others have shown that the conversion of 

 feldspar to serpentine is probable, I am not aware that any 

 definite proof of this change has been published. In the Coast 

 ranges it seems beyond a doubt. The feldspars are corroded 

 externally, cracks are widened irregularly and filled with 

 serpentine, and in some cases elongated teeth of serpentine may 

 be seen biting into the clear feldspathic mass. It is impossible 

 to explain these and many similar occurrences except on the 

 supposition that a reaction between some fluid and the feld- 

 spars has yielded serpentine. 



That quartz is sometimes converted into talc is a well known 

 fact. In the altered sandstones of the Coast Ranges it is con- 

 verted into serpentine. The proof is similar to that of the 

 transformation of other minerals. In one very beautiful 

 instance a clastic quartz grain of characteristic form, full 

 of fluid inclusions, and containing an imbedded apatite 

 microlite has been attacked from the outside. The original 

 outline is preserved, but the outer layer of the fragment is now 

 entirely occupied by felted fibers of serpentine and in addition 

 long, slender, green needles pierce into the quartz toward its 

 center. That there might be no doubt as to the character of 

 this occurrence, the slide was uncovered and a second entirely 

 similar, but less beautiful instance was chemically tested. 



* Without entering here upon any review of the serpentine controversy, it may 

 he noted that although the hypothesis that serpentine is substantially a result of 

 the alteration of olivine seems to have been based chiefly upon the investigations 

 of Professors Sandberger and Tschermak, published in 1866-7, Sandberger 

 recognized the formation of serpentine from the hornblendic rocks and diabases, 

 and Tschermak describes the conversion of enstatite to serpentine. Dr. Hunt 

 also admits the derivation of serpentine from enstatite in some cases. 



