A'U. 1882 PVRITli CAKKVIM. r,:)Ll) AXU GALENA POGUli 479 



has figured and described natural etchings on p3'rite from Traver- 

 sella, Italy, which are somewhat similar to the ones here depicted. 

 At times the gold crystals or small rounded knobs of galena are 

 situated upon small six-sided pedestals composed of laminae of pyrite 

 bounded by two pyritohedron and four octahedral planes. The above 

 features may be seen by referring to plate Lix, figure i. 



CrystallograpJiy of the gold. — The gold crystals are most abundant 

 on the face shown in plate ijx, figure i, though some are present 

 on each of the other faces. They are usually from one-third to one- 

 half buried in the pyrite. nevel- more, and seem to have no definite 

 orientation in regard to their host. Most of them show crystal 

 outline and many are rather synmietrically developed ; their average 

 diameter is about i mm. The faces are slightly convex, without 

 bright luster, and the edges are not sharp. No measurements were 

 attemptefl on the goniometer, as the crystals were not fitted for giv- 

 ing reflection, nor, indeed, could they be easily plucked from their 

 settings. The following forms, however, by aid of a hand lens, were 



Fig. 82. — The most common shapes of the gold crystals. Enlarged octahe- 

 dron ; combination of cube and octahedron ; combination of octahedron and 

 •dodecahedron ; combination of octahedron and trapezohedron. 



positivelv determined: cube, a (lOo) ; octahedron, o (m) : dodeca- 

 hedron, d (no), and trapezohedron, n (211) or m (311). To these 

 should be added a hexoctahedron as probably present, this form pos- 

 sibly corresponding to .r (18.10.1) described by Dana^ on gold from 

 California. The most common combinations, as shown in figure 82, 

 are : Octahedron, cube and octahedron, dodecahedron and octahedron, 

 and trapezohedron and octahedron. 



Crystallography of the galena. — The galena possesses three dis- 

 tinct habits, two of which have two or more appearances, due to 

 peculiarities of orientation : 



(i) Normal galena. A very small part of the galena has the 

 ■ordinary step-like appearance characteristic of this mineral and re- 

 quires no special description. This phase is arranged with one cubic 

 cleavage parallel to the cube faces of the pyrite, with the striations 

 on the latter intersecting diagonallv its other cleavages. 



° Dana, E. S. On the crystallization of gold. Am. Jour. Sci., vol. 32, 1886, 

 -pp. 132-138. 



