1906.] 



SMITH— PARAGENESIS OF MINERALS. ' 189 



a pale blue mineral with the optical orientation and the pleochroism 

 of glaiicophane, but evidently poor in iron. In default of analyses 

 of this variety it can not be assigned with certainty to gastaldite. 



Pargasite.—ln the basic eclogites of California the writer has 

 found a black amphibole resembling pargasite from Pargas, but 

 differing from that mineral in the orientation of its optical axes, and 

 in its pleochroism. This mineral has been analyzed and its physical 

 properties studied by Mr. W. O. Clark/ assistant in geology at 

 Stanford University. It fuses readily to a black globule, and colors 

 the flame yellow. It occurs abundantly in short, thick-set prisms 

 with a cleavage angle of about 124°. It is monoclinic, with parallel 

 extinction on planes in the zone of the symmetry axis, and on the 

 clinopinacoid gives an extinction of c A C about 18°. The axis of 

 least elasticity is nearest to crystallographic c. The plane of the 

 optical axes lies in the symmetry plane, and the a axis is the acute 

 bisectrix, hence the double refraction is negative. The absorption 

 is strong and the pleochroism decided, a = yellowish brown, jb = 

 deep olive green, and c = greenish blue. The absorption formula is 

 l)>C>a. The angle of the optical axes is very wide, being 



nearly 90°. 



This mineral was first mentioned by Mr. R. S. Holway,- and 

 by him doubtfully referred to pargasite. It is abundant in the 

 black eclogites of Calaveras Valley, Santa Clara County, and has 

 also been identified by the writer in a similar rock near Reed's 

 Station on the Tiburon Peninsula. It is associated with glauco- 

 phane, carinthine, actinolite, red garnet, epidote, margarite, albite, 

 and lawsonite, and is known in only those rocks that are unusually 

 rich in iron. In these rocks the glaucophane is a later product than 

 the pargasite, and appears only as a replacement rim around the 

 latter. Pargasite is most nearly related to an amphibole made 

 artificially in the wet way by Chrustschoff.-^ The artificial amphi- 

 bole was black, and showed strong pleochroism from yellowish 

 green to bluish green; c A C 17° 56', 2 y 82°, and sp. gr. 3.245. 

 a and t = yellowish green, and C = bluish green. There is a re- 



^ Unpublished paper. 



'Journal of Geology, Vol. XII. (1904), "Eclogites in California." p. 352. 



3 5m// Acad. Sci. St. Petersburg, 23 Oct., 1890; and Ncues Jahrb., 1891, 



Vol II , p. 86; cited by Hintze, " Handb. d. Min.," Vol. II., pp. 1232 and 1242. 



