﻿K S. Dana — Crystallisation of Native Copper. 417 



The only one of the above angles which could be measured 

 with really satisfactory precision was the inclination of two 

 opposite faces on the dodecahedral plane; these were found to 

 be 20° 59' and 21° 0', which correspond very closely with the 

 calculated angle 20° 52J-'. Also for 18-10'5^18'5-10 was ob- 

 tained 19° 14', required 19° 12J- / . On two of the specimens 

 the faces of this hexoctahedron were striated coarsely parallel 

 to the edge C, owing to the oscillatory combination of this form 

 with a second hexoctahedron approximating closely in position 

 to it. It was not possible to obtain a reliable symbol for the 

 second form. 



Another hexoctahedron is shown in fig. 12, which approxi- 

 mates closely to the dodecahedron. Many of the crystals on 

 the specimen giving this combination showed the dodecahedral 

 faces simply divided by faint striations into four fields. Other 

 crystals showed the hexoctahedron distinct, two faces, over 

 the tetrahexahedral edge (B), being in oscillatory combination 

 and hence producing a fine striation. In one or two cases the 

 faces were large and smooth enough to yield distinct images 

 with the compound goniometer, and in this way were obtained 



11-6-1 ^ 11-1'6=33° 12' and ll'6'l a11'6'1=9° 15'. 



The various angles for HG'l or 11-^ are : 



Edge A. Edge B. Edge C. 



11-6-1 ^ 11-1-6 ll'6-l* 11-6-1 11-6-1 ^6-11-1 



32° 40V 9° 1¥ 32° 40V 



Also 



100 ~ 11-6-1=28° 56V, HO* 11-6-1 = 16° 59f, 111 ^ 11-61=34° 14'. 



The agreement is close enough to establish the symbol given 

 as at least representing very closely the position of the form in 

 question. Some of the crystals of this specimen showed the 

 cube also as a prominent form. 



Still another hexoctahedron is exhibited by the twin crystal 

 figured on Plate XI (fig. 32). This form is interesting because 

 it is clearly the one whose oscillatory combination produces the 

 fine striation often observed on the faces of the tetrahexahedron 

 h. This fact fixes the ratio of two of the axes as 4 : 1 and the 

 measured angle on a, the only one obtainable with anything 

 like accuracy serves to establish as the probable symbol 

 12*32 (6-4), which, however, needs confirmation. 



10(U12-3-2=16 o 43V calculated, =16° 30 / measured. The 

 principal angles for this form are : 



Edge A. Edge B. Edge C. 



12-3-2 ^ 12-2-3 12-3-2 /s 12-3-2 12'3-2 * 3-12'2 



6° 281' 18° 22V 60° 18$'. 



A number of the specimens showed more or less indistinctly 

 planes of one or more hexoctahedrons, but it was only rarely 



