﻿E. S. Dana — Crystallization of Native Copper. 415 



recent contribution to the subject in hand is that by W. G. 

 Brown in the last number of this Journal. The crystals de 

 scribed by him were artificial and showed some interesting 

 peculiarities of twinning structure. 



The list of forms thus identified upon crystals of native cop- 

 per is as follows : 



Cube a (100, i-i), dodecahedron d (110, i), octahedron o (111. 

 1); tetrahexahedrons h (410, z-4), / (310, i-8), & (520, *f)j 

 e (730, i-%), e (210, £2), d (740, i-%\ I (530, * |) ; trisoctahedrons 

 w (511, 5-5), fi (411, 4-4), m (311, 3 8); hexoctahedrons £ (421, 

 4.2)?,2/(18-10-5,Y-t), ^(531, 51). 



Through the kindness of Mr. Clarence S. Bement of Phila- 

 delphia, the writer has had an opportunity to make a careful 

 study of his beautiful collection of specimens of native copper 

 from Lake Superior, numbering upwards of sixty. A consid- 

 erable part of these were collected by Mr. Norman Spang, 

 whose exceptional opportunities in this direction, extending 

 over a number of years, were most zealously used ; to these 

 Mr. Bement has himself made many important additions. It 

 is not too much to say that these specimens taken together 

 form the finest collection ever made of the crystallized native 

 copper from this remarkable locality, while many of the indi- 

 vidual specimens are wholly unique. As will be seen from 

 the descriptions in the following pages the collection offers many 

 points of scientific interest and novelty. In addition to this 

 suite of specimens and a few others from foreign localities, the 

 writer has also had the use of a large number belonging to the 

 cabinets of Professor G. J. Brush and of the Yale College 

 Museum. These have served in some important respects to 

 supplement the Bement collection. 



List of planes observed. — The planes which have been ob- 

 served on the specimens named are: a, d, o; tetrahexahedrons 

 h, k, e, I; trisoctahedrons m, n (211, 2-2); hexoctahedrons y, 

 x (11-6-1, ll-V-)> 2(12-3-2, 6-4)?. Of these w, x, z are new to 

 the species. 



Description of simple forms. — Figures 1 to 12, on Plate X, 

 show the more important of the simple forms in their normal 

 symmetrical development, which have been observed on the 

 Lake Superior specimens. Decidedly the most common type 

 is that of the tetrahexahedrons, and of the four included in the 

 above list h and lc occur most frequently, especially the former. 

 This form A (410, z-4) is shown alone in fig. 4; it is the most 

 obtuse of the tetrahexahedrons observed on this species and 

 thus approximates most nearly to the cube; its interfacial 

 angles (supplement) are: over #=28° 4', over d=61° 56', and 

 over the edge A (410 ^401) = 19° 45'. Fig. 6 on the other 

 hand gives the tetrahexahedron I (530, t-f), which approaches 



