Penfield and Ford — Calaverite. 227 



seemed to promise the best results, and which was selected 

 first of all for study, is represented in orthographic projection 

 upon the clino-pinacoid by figure 2, page 229. It was apparent 

 on inspection that certain faces, m, s, q, o, and^?, occurred in 

 pairs, as demanded by monoclinic symmetry, and the mono- 

 clinic character was fully substantiated by measurements. Two 

 of the forms, m and p, to which the symbols (110) and (111) 

 are assigned, agree very closely with corresponding forms on 

 sylvanite, as shown by the following comparison : 



m ^ 



m\ 



110 



/\ 



110 



Cala 

 = 63° 



vrerite. 

 1'* 



Sylvanite 

 62° 56' 



P * 



P 



111 



/\ 



III 



— 93 



49 



94 30 



m ^ 



P 



110 



/\ 



111 



= 36 



3S* 



37 3 



m! ^ 



P 



110 



/\ 



111 



= 68 



45* 





Taking the measurements marked by asterisks as funda- 

 mental, the following axial ratio has been calculated, with 

 which, for comparison, that of sylvanite is also given : 



Calaverite, a : b : c — 1-6313 : 1 : 1-1449 ; /3 — 89° 47^' 

 Sylvanite, " " = 1-6339 : 1 : 1-1265; @ = 89 35' 



As will be shown later, the forms m and^> occur on most of 

 the crystals, and, with the exception perhaps of the form let- 

 tered o, they are the most prominently developed of the termi- 

 nal faces. We feel, therefore, that the choice of these as 

 the unit prism m (110) and the unit pyramid p (111) is the 

 best that can be made, especially as the axial ratio derived 

 from them is so nearly like that of sylvanite. Taken in con- 

 nection with the similarity in chemical composition between 

 calaverite and sylvanite, it does not seem probable that such 

 close agreement in crystalline characters is wholly a matter of 

 accident. 



Thus far the crystallization of calaverite seems simple and 

 satisfactory ; beyond this point, however, the results are almost 

 startling from a crystallographic standpoint, since but few of 

 the many faces observed have simple indices. As no possi- 

 bility of simplifying the symbols has presented itself to us, it 

 has been decided to give our results in such a form that they 

 may be made use of by others, and we will ask our readers to 

 reserve their judgment of our interpretation of the crystals 

 until the results have all been presented. 



Peculiarities of Crystallization: Method of measuring. — 

 Although the crystals are highly modified, a scarcity of zonal 

 relations among the terminal faces is noticeable. The only 

 prominent zone is that of the forms lettered D, p, o, q and s, 

 figure 2 et seq., also shown in the stereographic projection, 



