18 



PROCEEDINGS OF THE NATIOISTAL MUSEUM 

 Angles of diopside crystal, Figure 2 



VOL. 71 



Although no optical properties were measured or no analyses 

 made upon material of the last-described specimens, they are prob- 

 ably very similar in composition to the foregoing. 



SAHLITE 



While most of the pyroxene of this locality consist of nearly pure 

 diopside, there are several specimens which are largely made up of 

 another memljer of the diopslde-hedenbergite series shown by its 

 optical properties to be somewhere near midway between these two 

 end members. 



The principal lot of these specimens (No. 84565) contains several 

 large masses almost entirely composed of blackish green pyroxene 

 varying from massive granular material to prismatic crystals of 

 simple habit up to 4 by 10 mm. in size, which project into open spaces 

 or into calcite which fills part of the vugs. In the empty vugs a 

 few scattered whitish apatite crystals rest upon and are evidently 

 later than the sahlite. Optically this pyroxene is biaxial and positive 

 with 2V large, dispersion r > v, perceptible. Under the microscope 

 it varies slightly from pale brownish-green to blue-green, the latter 

 probabl}'^ being the original tint, the brown being due to incipient 

 oxidation. It shows good cleavage. The maximum extinction 

 measured on crushed fragments is 44°. The refractive indices meas- 

 ured are j3=l.QdO, y= 1.715. The crystal habit is illustrated in 

 Figure 5. In some cases the crystals are sheathed with an outer 

 coating of actinolite, the fibers of which parallel the vertical axis of 

 the pyroxene crystal. The crystal which was measured gave the 

 following angles: 



