364 



University of California Publications. 



[Geology 



In the California]! rocks I have met with many glaucophane- 

 like amphiboles very faintly colored, with small angle of extinc- 

 tion and variable axial angle, but as we have no analyses of them 

 I do not know if they may be identified with gastaldite. In fact, 

 there was no difference from the gastaldite of St. Marcel, etc. 

 (slides in collection of Dr. Palache), which I have investigated. 



As type of the glaucophanes for the Californian rocks, I con- 

 sider the blue hornblende from North Berkeley (XI) described 

 and analyzed by W. C. Blasdale.* I had the opportunity of 

 seeing the original specimens, and of verifying and completing 

 the optical determination of Blasdale. Pleochroism brillant: C 

 = azure blue, fa = violet to purple, a = yellowish to colorless; 

 C ^> fa > 3. Angle of extinction on elinopinacoid, C:c = -b°; 

 on cleavage lamellae about -8° (in the most deeply colored even 

 more) ; birefringence as usual; 2 V not very large. The first 

 bisectrix (negative) is almost perpendicular to the orthopinacoid. 



Blasdale has, however, analyzed another glaucophane (XII) 

 which is in some respects different from others. It is a very dark 

 blue-violet glaucophane, which occurs in large prisms apparently 

 homogeneous and pure, but showing under the microscope many 

 patches of green amphibole (actinolite or karinthine) just as in 

 erossite described by Palache. Sp. gr. 3.119-3.116. Pleochro- 

 ism: t = dark Prussian blue, fa = intense violet, a = yellowish; 

 C ^> fa> 3. Angle of extinction on elinopinacoid, -8°, on cleav- 

 age lamellae, -11° but variable with the intensity of the color; 

 in some faintly colored specimens only -9°, in others very in- 

 tensely colored up to -13°. It extinguishes in the same direction 

 as the green amphibole, which has an angle of extinction of -18°. 

 Birefringence : y — a = 0.018, somewhat smaller, y — /3, how- 

 ever, very small ; 2 V very small, some lamellae being uniaxial 

 negative. The axial plane is parallel to the plane of symmetry, 

 the first (negative) bisectrix being almost perpendicular to (100). 



The analysis indicates, as compared with the former, a de- 

 crease in A1 2 3) and some increase in Fe 2 3 . The increase of 

 Na 2 compensates for the decrease of MgO and CaO. 



Glaucophanes with very small optic angles, or sometimes even 



* W. C. Blasdale. Contribution to the Mineralogy of California. Bull. 

 Dept. Geol. Univ. Cal., 1901, 2, p. 327. 



