S. L. Penfield — Bertrandite from Colorado. 5 5 



polarizing microscope but it was too small and fragile to trans- 

 fer and use in the axial angle apparatus The acute bisectrix 

 is axis of greatest elasticity and the double refraction is there- 

 fore negative. 



The hardness of the crystals is 6-7. They scratch feldspar 

 readily, and with care can be made to scratch quartz, though 

 they are apt to crush owing to their small size and good cleav- 



The specific gravity, taken with the Thoulet solution, is 

 2-598. Bertrand found 2*593, Damour 2-586, and Scharizer 2'55. 



By sacrificing all but one of the small crystals and scraping 

 off the remnants of broken crystals from the quartz I succeeded 

 in obtaining 0*1259 grams of material which floated on the 

 Thoulet solution at 2*610 and sank at 2 '551 sp. gr. This 

 was subjected to a very careful chemical analysis with the fol- 

 lowing results : 



Penfield. 



Damour. 



Theory 



for H 2 Be 4 Si 2 0< 



Si0 2 51-8 



49-26 





50-42 



BeO 39-6 



42-00 





42-02 



CaO 1-0 









H 2 84 



6-90 





Y-56 



Fe 2 3 



1-40 







100-8 99-56 100-00 



The .analysis is satisfactory considering the small quantity of 

 material at my command. The BeO which was precipitated 

 with ammonia was free from alumina and gave the character- 

 istic beryllium reactions. The mineral lost 0*5 per cent by 

 drying at 100° C. and 1*40 per cent at a faint red heat. The 

 water in the analysis is too high, and probably part of it does 

 not belong to the composition of the mineral. The micro- 

 scopic sections show liquid inclusions, which are not C0 2 

 and are probably water, which may account for some of the 

 excess. 



It is probable that further search at Mt. Antero will yield 

 more specimens of this mineral and better material for study. 

 It is interesting to find this rare mineral in America along 

 with the phenacite and beryl. 



In closing I take especial pleasure in expressing my thanks 

 to Mr. W. B. Smith for giving me the specimen for carrying 

 on this investigation. 



Mineralogical Laboratory, Sheffield Scientific School, May 14, 1888. 



