Mr. L. Fletcher's Crystallograpliic Notes. 183 



A fifth specimen, from the same locality, presents some very 

 sharply defined crystals associated with massive copper, native 

 silver, and calcite. The crystals present a symmetrical deve- 

 lopment of the combination (5 3 0) (5 3 1) (1 0), as shown 

 in fig. 2. The angles were measured with the hand-gonio- 

 meter : — 



Observed. Calculated. 



035.053 ... 27i 28 4 



351.351 . . . 19f 19 28 



351.350 . .;../ ... 10J 9 44 



The remaining specimens to be mentioned are all spinel-like 

 twins, and are much shortened along that trigonal axis which 

 is perpendicular to the twin-plane. 



A specimen from Lake Superior presents some large crys- 

 tals drused with quartz. One of the smaller and very sharply 

 defined crystals was shown by help of the reflecting goniometer 

 to be a spinel-like twin of the combination (1 0) (11 0) 

 (7 30). 



Observed. Calculated. 



07 3.037 .. 43 14 43 36 



037.001 . . 23 5 23 12 



037.307 . . H \ 2 7 j 32 21 



The remaining specimens are from the Eelistian Mines, 

 Cornwall. 



The first specimen is a dendritic aggregation of crystals, 

 mostly indistinct. One crystal, however, from which good 

 measurements could be obtained, proved to be a spinel-like 

 twin of the combination (111), (7 40), having the habit 

 shown in fig. 3 ; in which the lines formed by the recurrence 

 of dots and dashes denote reentrant edges : — 



Observed. Calculated. 



740.740 . 



. 60 2 



59 30 



740.470 . 



. 31 



30 30 



111.740 . 



. 38 3 



38 li 



740-704 . 



41 221 

 ' 41 52 J 



41 4 



It will be seen later that this form (7 4 0) is also presented 

 by crystals of native silver from Chili. 



The second and third specimens present crystals which are 

 spinel-like twins of the combination (111) (210) (511) 

 and have the habit shown in fig. 4. The faces of the form 



