Penfield and Ford — Calaverite. 



235 



crystal may be regarded as the best we have 

 Without a two-circle goniometer it would have 

 been almost impossible to have measured more 

 than a few of the angles of such a small crystal. 

 With a two-circle goniometer, on the other hand, 

 the measurements were made without difficulty. 

 Altogether seventeen terminal faces were observed 

 on this crystal, the area of whose cross-section is 

 less than that of a hyphen on this printed page. 

 The crystal, which is the most symmetrical in its 

 development of any we have seen, is represented 

 with ideal symmetry in figure 20. The clino- 

 pinacoid b (010) is present, and monoclinic sym- 

 metry is proved by the occurrence of the forms 

 m, o,p r f, and s as pairs of faces, making in each 

 case almost identical angles on either side of 

 (010), as indicated by the horizontal circle 

 measurements. A complete list of the angles 

 measured on this crystal is given in the following 

 table : 



examined. 



20 



Pttlc 







Measured. 



Calculated. 

















Symbols. 



Vertical. 



Horizontal. 



Vertical. 



Horizontal. 



b 



010 



00° 00' 



00° 00' 



00° 00' 



00° 00' 



m 



110 



u 



31 32 



a 



31 30J- 



771 



110 



u 



31 32 



a 



31 30* 







. 13-22-10 



47 10 



28 12 



47 30-J 



28 18 







13-22-10 



a 



28 2 



a 



28 18 



p 



111 



54 57 



47 8 



54 48 



46 54£ 



p 



111 • 



u 



46 41 



a 



46 54| 



f 



112 



70 21 



61 37 



70 29 



61 40 



f 



112 



u 



61 36 



u 



61 40 



9 



4*7-10 



73 53 



52 46 



74 7 



52 22 



V 



2-11-10 



82 17 



38 25 



81 48 



38 44 



k 



10-32-21 



108 27 



31 3 



108 18 



31 6 



It 



11-18-10 



127 21 



30 52 



127 32 



31 28 



u 



11-18-10 



(i 



31 00 



u 



31 28 



X 



11-20-6 



143 52 



22 36 



142 4 



23 5 



s 



11-62-6 



a 



7 52 



a 



7 50 



s 



11-62-6 



a 



8 00 



a 



7 50 



B, 



17-0-2 



9 26 



90 00 



9 30 



90 00 



B : 



17-0-2 



9 45 



a 



a 





D 



3 4 



63 38 



a 



62 4 





H 



5-0-11 



72 11 



a 



71 36 





I 



2-0-11 



82 25 



a 



82 25 





P 



II-0-2 



165 58 



a 



165 28 





P 



11-0-2 



165 26 



it 



tc 





