﻿416 E. S. Dana — Crystallization of Native Copper. 



nearest to the dodecahedron, it is interesting to note that its 

 angles over a and d respectively are the same as those of h 

 over d and a. The form h is usually combined with the cube 

 (fio-. 5) or with the cube, dodecahedron and octahedron (fig. 7) ; 

 not infrequently h and h appear together both beveling the 

 cubic edges (fig. 8). In fig. 9 we have the dodecahedron modi- 

 fied by the planes of this same tetrahexahedron. The faces of 

 h are commonly striated in a direction normal to the cubic 

 edges owing to an oscillatory combination of the planes of a 

 hexoctahedron which, as noted later, has probably the symbol 

 12-3*2 (6 4). Not un frequently, however, the faces of h are 

 smooth and free from striations. The form k also occasionally 

 shows similar striations. 



Of the primary forms of the system, the cube alone is a 

 rather common occurrence, and the dodecahedron occurs though 

 less frequently. The octahedron by itself, however, is not 

 represented at all on the specimens in hand; this may be due 

 in part to accident but seems to show that the octahedral form 

 alone is at any rate much less common than is the case with 

 the other isometric native metals. Fig. 1 gives the nearest 

 approach to the simple octahedron observed, and in fig. 11 the 

 octahedron is shown modified by the hexoctahedron y. The 

 octahedron is also prominent in the complex crystalline growth 

 shown in fig. 48. 



Fig. 2 represents the only case in which the trisoctahedron 

 m (311, 3 3) was observed ; this, as will be remembered, is a 

 very common form with gold. Fig. 3 shows a combination, 

 which will be recognized at once as the common garnet form, 

 it is, however, very rare with this species and is only repre- 

 sented by one specimen. The faces of the trisoctahedron are 

 slightly uneven with the tendency to striation common with 

 the species, and hence no exact measurements were possible. 

 The true symbol is obvious, however, since these faces truncate 

 the edges of the dodecahedron ; strictly it should perhaps be 

 said that the symbol 211 (2-2) is the one toward which the 

 form closely approximates. 



Fig. 10 illustrates a type of crystal represented by several 

 specimens and similar to that described by vom Eath ; it is a 

 dodecahedron with the planes of the hexoctahedron y (18-10-5, 

 JL8L-S.Y This symbol was assigned by vom Eath with some 

 question, as his measurements were not very precise, but the 

 writer's observations go to confirm his conclusion. The angles 

 of the hexoctahedron are as follows : 



Edge A. Edge B. Edge C. 



18-10-5 ^18-5-10 18-10-5 a 18-10-5 18-10-5 a 10'18'5 



19° 12£' 27° Iff 30° 58' 



Also 



100 a 18-10-5=31° 50r, 110 a 18-10-5=20° 52^, 111 a 18-1 0-5=36° 44*'. 



