490 S. L. Pen field — Beryllium Minerals from Colorado. 



lation from the above symbol are 12° 52' and 46° 15' using 

 Kokscliarow's length of the vertical axis c=0498S6. A single 

 one of these pyramids, lettered X, in combination with the 

 hexagonal prism ?n, I, 1010, is shown in fig. 1. The 

 obtuse angle of this pyramid is usually truncated by 

 a pyramid of the second order 12-2, 6"6*12'1, the 

 crystal which was measured giving five faint re- 

 flections instead of the possible six, but the faces 

 which are very small are not represented in the 

 figure. Reflections were also obtained from other 

 steep pyramidal forms but they were always faint 

 and could not be referred to definite forms. In 

 addition to the above steep pyramidal forms some of 

 the etched crystals show very distinct facets of a 

 pyramid of the first order making, in two cases which 

 were measured, angles of 40° 31' and 40° 58' with the 

 prism and corresponding to the pyramid 2, 2021 the 

 calculated angle being 40° 5.7^'. These do not ap- 

 pear as a single pyramid but as a group of pyramids 

 and they occur along with the steep dihexagonal forms on the 

 same crystal. After seeing these beautiful and undoubtedly 

 etched crystals from Mt. Antero there is little doubt that the 

 curiously developed beryl from Willimantic, Ct, previously 

 described in this Journal,* has resulted, as was suggested, by 

 the action of some solvent on a large beryl crystal. If so, the 

 forms thus far observed which have been produced by etching 

 in nature are as follows : 





Mt. Antero. 



Willimantic 



, Ct. 



12-f 



36 24 60 5 



6-1 



4261 



12-2 



6 6 12 1 



3-f 



2131 



2 



2 2 1 



4-1 



3141 







1 



1011 



It is not possible at present to state what solvent has attacked 

 and etched the beryl crystals. The occurrence of octahedral 

 fluorspar with the beryl has suggested that perhaps some 

 fluorine compound has served as a solvent, but as beryl is 

 attacked with great difficulty by hydrofluoric acid this would 

 probably have expended itself on some more readily soluble 

 silicate. 



2. Bertrandite. 

 A description of the occurrence and hemimorphic crystalli- 

 zation of this rare silicate, 2Be 3 Si0 4 , EI a O, has already been 

 given. f From the examination of a large number of speci- 

 mens it seems very probable that the beryllium of the ber 

 trandite was obtained from the decomposition and partial 

 solution of the beryl crystals. The growth of the bertrandite 

 before or along with that of the phenacite crystals is also a 



*III, xxxvi, p. 318. fThis Journal, xxxvi, 1888, p. 52, and xxxvii, 1889, p. 215. 



