﻿E. 8. Dana — Crystallization of Native Copper. 427 



the first the lines of growth (the " tectonic axes" of Sadebeck) 

 of the adjoining crystals or parts of crystals (sub-individuals) 

 are the cubic axes; in the second they are axes inclined 60° to 

 each other and generally coinciding with the diagonals of an 

 octahedral face, that is, the lines normal to its edges and bisect- 

 ing the facial angles. A third method, quite different from the 

 others, has also been observed. 



The first method is common with many isometric species, 

 and is represented here in several different forms. Thus one 

 specimen is made up of small cubes grouped in this way. In 

 another there are several series of octahedrons each having a 

 common vertical axis, and each octahedron made up of many 

 small partial octahedrons (like fig. 1), the whole specimen a 

 wonderfully delicate and beautiful arborescent growth. Figs. 

 48 and 49 show interesting cases of the same thing. In fig. 48 

 the predominating forms are the octahedron and dodecahedron, 

 though the terminal crystals are sometimes as complex as fig. 

 16. On this specimen we have sometimes a long wire with 

 projecting points of small octahedrons ; then more complex 

 growths with branchings and rebranchings, and again a close 

 even network of rectangular ribs. In fig. 49 the form involved 

 is the tetrahexahedron h (410, i-4) and the lines of growth are 

 uniformly the cubic axes; as will be inferred from the figure 

 the specimen is one of much beauty and interest. 



The second method of grouping is, however, the more inter- 

 esting, especially so in that the crystals taking part in it are 

 generally twins. Here the twinning-plane is the plane in 

 which the lines of growth lie and these axes are three lines 

 crossing at 60° and situated as described. The explanation of 

 an analogous method of grouping was given by Rose in his 

 description of the complex growth among the Siberian crystals 

 already spoken of. The Lake Superior specimens differ from 

 the Siberian in that, although the branching is also at 60°, the 

 directions are almost always those of the diagonals of the octa- 

 hedral face, not of the edges. This statement is true of all the 

 Lake Superior specimens the writer has had the opportunity to 

 examine with a single exception, while one beautiful specimen 

 from Siberia in Mr. Bement's collection agrees with the descrip- 

 tion of Rose. It may be noted here that Sadebeck describes 

 both these systems of " tectonic axes" as occurring in the den- 

 dritic growths of native silver, and he also mentions having 

 observed the diagonal method of growth himself in copper. 

 The Lake Superior specimen described by vom Rath is stated 

 to have conformed to the method given by Rose. 



An ideal representation showing the common method of 

 growth spoken of, of the trigonal cubic twins, is given in fig. 

 50. The actual forms are, however, most complex, for instead 



