S. L. Penfield — Crystallization of Herder ite. 331 



Among the specimens that were examined from the new 

 locality there were only a few small crystals that were well 

 adapted for measurement with the goniometer and these were 

 always so attached that only a part of their faces were devel- 

 oped. Some of the faces are curved and give uncertain re- 

 flections but the majority are good and they are very free 

 from vicinal planes, which are prominent on the Stoneham 

 herderite. In the description of the crystals the position 

 adopted by E. S. Dana* has been retained, and as far as pos- 

 sible, his system of lettering. 



The habit of the crystajs is shown in figures 1, 2 and 3. 

 Number 1 is drawn with 010 in front and No. 2 with 001 ver- 

 tical, these positions being chosen because they are best adapted 

 for showing the monoclinic symmetry. Figure 3 is a basal 

 projection and from this and the spherical projection, fig. 13, 

 the relations of the forms and the prominent zones can readily 

 be made out. The forms which have been identified are as 

 follows : 



a, 



100, 



i-l 



«. 



302, 



-H 



r, 



112, 



_l 



7c, 



122, 



-1-2 



h 



010, 



i-i 



*, 



032, 



|-i 



s> 



332, 



_ 3 

 2 



10, 



3-12-4, 



-3-4 



c, 



001, 







v, 



C31, 



3-1 



n, 



381, 



-3 



z , 



394, 



f-3 



in 



110, 



I 



s, 



061, 



64 



n, 



331, 



3 









Author d:b\C — 0-63075 



1 



0-42742 



Haidinger " " = 0-6261 



1 



0-4247 



Dana ^ " " = 0-6206 



1 



0-42345 



The axial ratio was calculated from the measurements which 

 are marked by an asterisk in the table of angles. For com- 

 parison the ratios derived by Haidingerf from the Ehren- 

 friedersdorf and by Dana from the Stoneham herderite are 

 also given. 



/3 = 89° 54' 

 /? = 90 

 /3 = 90 



The angle ft is very close to 90°, but there can be no mistake 

 about the monoclinic character of the crystals as indicated by 

 the development of the faces. As regards the forms, those 

 shown in fig. 1 are almost invariably present. The basal plane 

 c always yields good reflections and the edges which it forms 

 with the dome t invariably curve and taper to a point as they 

 approach the pyramid z, tig. 2. The edges between t and z 

 were always rounded, and this is especially true in the vicinity 

 where c, t and z approach one another. The pyramid z which, 

 owing to the curved nature, did not yield very satisfactory 

 measurements was surely identified by its location in the zones 

 m, e, k, t and m, v. The pyramids q and n are commonly stri- 

 ated parallel to their intersection edges. 



*This Journal, III, xxvii, p. 229, 1884. 

 f Phil. Mag., iv, p. 1, 182S. 



