238 Ford — Nept unite Crystals from San Benito Co., Col. 



forms found on the specimens from California are indicated by 

 open circles. 



Optical. — For the optical study of the material a thin sec- 

 tion was first cut parallel to the symmetry plane (010). On 

 examination between crossed nicols it was found that one 

 extinction direction was inclined to the c-axis of about 24° in 

 the obtuse angle /3, while the second direction of extinction 

 very nearly coincided with the «-axis making an angle of 1° 38' 

 above it in front. The direction of greatest elasticity of the 

 section corresponds to the extinction direction which nearly 

 coincides with the a-axis. The section showed very strong 

 pleochroism, the ray vibrating parallel to the direction a being 

 colored yellow while the one vibrating parallel to c was a deep 

 brownish red. These relations are shown in figure 6. Two 

 other sections were cut, each being normal to one of the 



Fig. 6. 



Fig. 7. 



Fig. 8. 





ted 





red 



-0- 



red 



yello 



extinction directions of the section parallel to o (010). In the 

 section normal to the ct-direction, or nearly normal to the a 

 crystallographic axis, it was noted that the extinction direction 

 which was parallel to the J-axis was the direction of greatest 

 elasticity in the section or the direction of intermediate elas- 

 ticity b of the mineral. This section showed in convergent 

 polarized light an interference figure with a large axial angle, 

 the optical axes lying in the symmetry plane of the crystal. 

 This section showed no marked pleochroism, rays vibrating 

 parallel to the two extinction directions being both colored a 

 dark red. These relations are expressed in figure 7. 



The third section was cut normal to the direction c deter- 

 mined in the section parallel to b (010) and in its orientation 

 was nearly parallel to c(001). This section showed an inter- 

 ference figure with the optical axes lying in the symmetry 



