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PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 71 



This albite is overlain by the quartz crystals which resemble topaz, 

 described below. The albite has the habit shown in the drawing. 

 Figure 11. 



10 



11 



Figs. 10-11. — Cra-STALs of Albite 



ANORTHITE 



Plagioclase feldspar very near the anorthite end of the series 

 makes up an important part of a number of specimens although 

 in none of these does it foim good or attractive specimens worthy 

 of inclusion in collections as anorthite. One group of specimens 

 containing the measured crystals of titanite and the best epidote 

 crystals consists largely of a translucent white mineral which is 

 the earliest material and makes up the cores of the specimens. 

 Optically this mineral is found to biaxial and negative ( — ) with 

 2V large, dispersion r < v strong, extinction highly inclined against 

 the cleavage. The birefringence is fairly low and the intermediate 

 index of refraction, /?, is 1.582±.002. This mineral is doubtless 

 anorthite. It preserves hollow molds up to 2 cm., on an edge of 

 their rhombic cross section, of a prismatic mineral which preceded 

 the anorthite but was subsequently removed. Later the anorthite 



