ZOiSITE FROM LOWER CALIFORNIA 



BY OLIVER CUMMINGS FARRINGTON 



While at San Diego, California, in the spring of 1905, the writer 

 obtained from Mr. Ernest Riall of that city several specimens of a 

 radiated mineral, collected by Mr. Riall at the Trace mine, in the 

 Juarez District of Lower California. This locality, according to Mr. 

 Riall, is situated sixty miles south of the international boundary. The 

 accompanying cut shows the appearance of a typical specimen of the 

 mineral. It occurs as divergent groups of long, prismatic crystals irreg- 

 ularly penetrating a matrix of a white, granular mineral. The length 

 of the crystal groups varies from one to three inches. Their form 

 is essentially conical, the angle of the cone being about io°. In coloring 

 the cones are pink peripherally, pass interiorly into nearly colorless 

 and at the center are brownish-gray. Their constitution of numerous 

 individual crystals is shown by elongated brilliant surfaces into which 

 they readily separate longitudinally, but transversely the cones break 

 as units. The cones as a whole are translucent, but small fragments 

 are transparent. No terminal planes can be observed on any of the 

 crystals. The longitudinal fragments show roughly prismatic bound- 

 aries, but it was found impossible, with a reflecting goniometer, to ob- 

 tain satisfactory measurements of the prismatic angles, since numer- 

 ous longitudinal striations produce long series of reflections. Besides 

 the striated planes, others not striated appear to be cleavage planes 

 to the brachypinacoid. The longitudinal fragments are colorless and 

 transparent and show in polarized light extinction parallel to the long 

 axis. No pleochroism is observable. The character of the double 

 refraction is positive. In convergent light the emergence of an optic 

 axis may be seen on such fragments. Sections perpendicular to the axis 

 of the cone are colorless and show no pleochroism. Numerous cleavage 

 cracks making angles of 53 with each other penetrate such sections. 

 Between crossed nicols a polysynthetic twinning structure is seen to 

 characterize the whole, the field being filled with lamellae in parallel 

 position. These lamellae divide into two groups as regards width, 

 the broader being from .1 to .07 mm. and the narrower from .025 to 

 .012 mm. The broad and narrow lamellae alternate. The direction 



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