i9o6.] SMITH^PARAGENESIS OF MINERALS. 229 



albite in veins or patches, and the rest is taken up by the ferro- 

 magnesian minerals to form glancophane, or when soda is deficient, 

 carinthine or pargasite. In the aluminous calcium augite there was 

 more lime than was needed for the formation of glaucophane, and 

 epidote was produced in considerable quantities, but when the ori- 

 ginal minerals were olivine or orthorhombic pyroxene there was no 

 excess of lime. Thus in the metamorphics made from rocks of the 

 nature of peridotites epidote and garnet are rare, while they are 

 plentiful in those made from diabases and diorites. 



When the amount of iron was higher than was needed for the 

 glaucophane, and the lime too low for lawsonite, the iron-alumina 

 garnet was formed, as in the black pargasite, and green actinolite 

 and omphacite eclogites. And when the iron, alumina, lime and 

 soda were all abundant, then glaucophane, red garnet, lawsonite and 

 epidote were all formed together, as in the Tiburon eclogite. All 

 this, of course, refers only to the predominating minerals, since in 

 any of the metamorphic rocks of the basic series small quantities 

 of either glaucophane, lawsonite, garnet, or epidote may occur. 



Near the Searsville dam in Santa Clara County is a diorite in 

 which the metamorphism is fundamental, every mineral in the rock 

 being secondary, and yet the rock is still recognizable as a diorite. 

 It is composed of carinthine, epidote, white mica, probably paragon- 

 ite, albite, and abundant quartz, with titanite and pyrite scattered 

 through the mass. A little glaucophane appears as replacements 

 of the carinthine. The original plagioclases have been almost en- 

 tirely decomposed, and the hornblende or pyroxene remade into 

 carinthine by losing titanium and taking up part of the albite mole- 

 cule from the plagioclase. No lawsonite nor garnet was made out 

 of the anorthite molecule, but abundant epidote instead. This for- 

 mation of more basic minerals has set silica free, and this has crys- 

 tallized out as quartz in veins and patches all through the rock. 

 As there was too much albite in the original feldspar for the needs 

 of the carinthine and glaucophane, albite has crystallized out in veins, 

 and the residue of the molecule took up alumina and formed paragon- 

 ite. The crystals of pyrite in the mass tell of the nature of the 

 solutions that aided in the readjustment. 



On Oak Ridge in Santa Clara County, about five miles east of 



