186 SMITH— PARAGENESIS OF MINERALS. [Octobers, 



Original hornblende has been observed in the altered quartz 

 diorite of the Oak Ridge, where it shows all the characters of the 

 titaniferous kataphorite. This has been decomposed around the 

 borders, with the addition of soda to form glaucophane (crossite), 

 and the setting free of titanium to form leucoxene, and titanite. 

 Most of the hornblende of the pseudodiorites and pseudodiabases 

 is not original in the strictest sense, for it is largely uralite after 

 augite, but it was already present before the metamorphism which 

 later formed epidote and glaucophane in these rocks. 



Quartz is present as an undoubted original constituent only in 

 the quartz diorite, but much of the quartz in the siliceous glauco- 

 phane schists may be original, since there is no criterion by which 

 the original granular quartz may be distinguished from the same 

 mineral when recrystallized. 



Original augite is present only in the pseudodiabases and 



pseudodiorites, and a few greenstones, where the metamorphism has 



not gone very far. 



Secondary Minerals. 



Of all the constituents of the metamorphic rocks of the Coast 

 Ranges of California glaucophane is the most characteristic. There 

 are probably several varieties of it, but at present it is not practicable 

 to separate them. In all the true glaucophanes in these rocks there 

 are certain general characteristics that distinguish them. The 

 vertical axis is the axis of least elasticity, the extinction angle of 

 c A C is small, ranging from 5° to 14°. The character of the double 

 refraction is always negative, and the plane of the optic axes lies 

 in the ©lane of symmetry. The angle of the optic axes in some 

 varieties is so small that the mineral is almost uniaxial, in others the 

 angle is moderately wide. The pleochroism is always strong, the 

 light vibrating parallel to a being pale yellowish, that parallel to !) 

 deep violet, and that parallel to C intense sky blue. The crystal 

 faces are extremely simple, only three distinct forms being seen, 

 the orthopinacoid (100), the prism (no), and the clinopinacoid 

 (010). The crystals are usually in long prisms after (no) rarely 

 showing the other faces. 



This mineral is equally at home in the acid quartzites, altered 

 diorites, diabases and gabbros, so the acidity or basicity of the 



