ECLOGITES IN CALIFORNIA 357 



to 10 or 12™"^ for the rounded forms in some of the Calaveras expos- 

 ures. Of the essential minerals garnet is evidently the oldest, for in 

 the cracks are found glaucophane, omphacite, and hornblende. Yet 

 these latter minerals are also found as inclusions together with rutile, 

 apatite, feldspar, and quartz. Inclusions of glaucophane may be 

 paramorphs of inclusions in the original matrix. Qualitative tests 

 indicate that the garnets contain iron, calcium, and aluminum. 



Omphacite, the light green augite, usually occurs in aggregates of 

 prismatic crystals, some a ^™"' in length and without definite termi- 

 nation. The bright polarization, absence of pleochroism, high 

 extinction angle, and occasional augite cleavage serve to distinguish it. 

 Liidecke deduced the formula (CaFe) Si03MgSi03 from his chemi- 

 cal analyses. 



Smaragdite is an emerald-green actinolite that in the eclogites 

 much resembles omphacite, being distinguished from it by the horn- 

 blende extinction angle and usually by pleochroism. The blue soda 

 hornblende, glaucophane, has the marked pleochroism already given 

 and an extinction angle of C on c' varying from 5 to 15°. It seems 

 to be derived from hornblende in the eclogite in Calaveras Valley — 

 at least the hornblende crystals are bordered by it. Diller has already 

 been quoted as to the change of pyroxene to glaucophane in the Port 

 Orford rocks, some of which are here classed as eclogites. The 

 analyses of some of the igneous rocks considered show that they 

 contain enough soda for this change to occur without the addition 

 of elements from the outside. The hornblende in the Calaveras 

 eclogite show soda in the qualitative test, and also has a general 

 resemblance to glaucophane in its pleochroism and in its orientation. 

 Hintze has already been quoted in regard to a black pargasite that 

 seems to agree closely with the Calaveras variety of hornblende in 

 pleochroism and extinction angle. This pargasite contains, according 

 to his analysis, 3.44 per cent, of soda — which is more than the per- 

 centage of soda in the Port Orford glaucophane. 



Both garnet and hornblende are found replaced by chlorite — 

 pale green in color, and showing low interference colors except in the 

 Pennine variety, which shows Prussian blue between crossed nicols. 



Mica seems to be absent from the Calaveras slides and is found in 

 very small quantities in those from San Martin. In the Tiburon 



