428 Pratt — Crystallography of the Montana Sapphires. 



Bauer* has described etching-figures that he observed on the 

 base 0001 and the pyramid 2253 of the Burma rubies. Those 

 on the base are similar to the figures in fig. 5, except that the 

 outside contour of the rhombohedron is rounded. 



Sapphires from Emerald Bar, Montana. 



The crystals from Emerald Bar, Canon Ferry, Meagher Co., 

 Montana, are entirely different in their development from those 

 from Yogo Gulch. The prism $(1120) is always present and 

 is usually in combination with the base c(0001) and the unit 

 rhombohedron, /•(1011), fig. 17. On some of the crystals, how- 

 ever, the rhombohedron is wanting and the prism is very short 

 as represented in fig. 16. Fig. 15 represents a crystal termi- 

 nated by a pyramid of the second order in addition to the base 

 and rhombohedron. The measured _angles only approximate 

 to the calculated ones for the face 2243, but as this is the com- 

 mon pyramid for corundum it seems very probable that it is 

 the face. The crystal was only well terminated at one end. 

 The crystal is similar to one figured by Bauer from the Burma 

 district. 



The crystals are all rough and more or less striated, so that 

 the measurements with the contact goniometer were only 

 approximate, but were sufficiently accurate to identify the 

 faces. 



The repeated growth described above was also observed on 

 the Emerald Bar crystals but not in any variety of forms. 

 Only one form of growth was observed, represented in fig. IT, 

 page 427, which is 'a combination of the unit rhombohedron 

 and the base. 



None of the etching-figures so common on the Yogo Gulch 

 crystals were found on these crystals. 



Mineralogical Petrographical Laboratory, 



Sheffield Scientific School, New HaveD, Conn. 



* L. c, p. 213. 



