214 S. L. Penfielcl — Crystallized Bertrandite. 



and e at the other. This can be explained most readily by 

 considering the crystal as hemimorphic in the direction of the 

 vertical axis. As in our ordinary crystallographic projection 

 the figures of our crystals are very much fore-shortened in the 

 direction of the brachy axis d, and as the bertrandite crystals 

 are elongated in this direction, I have re-drawn fig. 1 making 



a the vertical axis, c the front and leaving b unchanged as in 

 fig. 1«, which gives a very good idea of the crystals. Figures 

 2 and la drawn the same as above represent a more highly 

 developed crystal. The most conspicuous faces on these crystals 

 are c and d above, both of which are highly polished and give 

 good reflections. The faces at the other end of the c axis are 

 by no means as good, the luster is poor and the faces oscillate 

 and combine with one another in such a way that the edges are 

 not sharp and continuous ; this is especially the case when x is 

 present. The x faces are not sharp and well defined but round 

 off the ends of the crystal in such a way that they do not form 

 straight edges with g and e ; they gave also no sharp reflection 

 of the signal with the goniometer. Approximate measurements, 

 however, and the occurrence of the faces in the zone d , and h 

 determine its indices to be I62 (3-6). The brachy-pinacoid b 

 gave fairly good reflections, h was in all cases small and gave 

 faint reflections. One twin crystal was observed, the basal 

 plane being the twinning plane and the d faces making a 

 very prominent reentrant angle. The crystals are usually at- 

 tached at one end of the brachy axis and as only one of the 

 bright d faces is conspicuous they have a very decided mono- 

 clinic appearance. In one of the detached crystals part of a sec- 

 ond d face was present developed as in the figures and showing 

 that the crystals are truly hemimorphic and not monoclinic. 

 In detaching one of the crystals a very perfect cleavage parallel 

 to b was developed which has not been observed before ; the 

 highly perfect prismatic and basal cleavages were also observed, 

 the same as in the Mt. Antero crystals. If we take the best 

 measurements which were obtained, 



c~d, 001 ^ 102 = 27° 42' and 

 m^m, 110 * ll0=59 = 16', 



the latter being cleavage faces, we obtain the axial ratio given 

 below, while for comparison the ratio obtained from the Mt. 

 Antero mineral is also given : 



Stoneham, Me. c: b: a = 0-5973: 1 : 0-5688 

 Mt. Antero, Col. c : b : a = 0-5953 : 1 : 0-5723 



I am inclined to give the preference to the measurements on 

 the Stoneham crystals ; if so, the angles which have been meas- 

 ured and the calculated values are as follows : 



