W. H. Hobbs — Goldschmidtite, a New Mineral. 363 



Crystal IV (fig. 4) is doubly terminated and represents a simple 

 twin with the twinning plane the orthopinacoid. One of its 

 individuals (the front one in the figure) displays the forms a, 

 b, m,f, t, n, .s, N", S, and Tc. The other individual differs in 

 having only one positive orthodome (N) and the form w in 

 place of n. Crystal V (fig. 5) is also a twin crystal, on the 

 front individual of which are developed the forms a, b, m, c, k, 

 and s. The other individual exhibits in addition n and lacks 

 the basal pinacoid. A small pyramid lying between k and s I 

 was unable to determine. All the crystals show a remarkably 

 perfect cleavage following the plane of symmetry. 



Cry st alio graphical Affinities of Goldschmidtite and Sylvanite. 



As might be expected from its chemical relationship to syl- 

 vanite, the mineral Goldschmidtite exhibits affinities also in its 

 crystal development. Both minerals have monoclinic sym- 

 metry and somewhat similar 

 forms are developed upon 

 them. Ten of the twenty- 

 two forms discovered on 

 Goldschmidtite have repre- 

 sentatives on sylvanite. Be- 

 low are given in parallel 

 columns the crystallograph- 

 ical constants of the two 

 minerals and some of the 

 angle readings between faces 

 of corresponding forms. It 

 will be noted that the dif- 

 ferences are greatest in the 

 prism zone, where the largest 

 faces of Goldschmidtite make the error of reading compara- 

 tively small. The orientation of sylvanite is that of Schrauf, 

 which is now generally adopted. 



The axes a and 6 are each about one-seventh longer in Gold- 

 schmidtite than in sylvanite. It is to be regretted that satis- 

 factory material is not available for the crystallographical study 

 of calaverite. That studied by Penfield* was so poor that he 

 was unable to determine the crystallographical constants. He 

 thinks the mineral is probably triclinic, with its angles some- 

 what similar to those of sylvanite. It lacks the pinacoidal 

 cleavage of that mineral but is observed in twins according to 

 the face of (101). When suitable material is available for' 

 study it will be interesting to see whether relations between 

 the lengths of the crystallographical axes and the proportions 



*1. c, p. 135. 



