28 Van Horn — Silver, Copper, and Cobalt Minerals. 



with silver in some places. The mineral was examined both 

 by the wet method and the blowpipe, and distinct tests for 

 bromine were obtained, although chlorine is certainly largely 

 in excess. Nevertheless, the combined evidence of the chemi- 

 cal tests and the bright yellow color lead to the conclusion that 

 the mineral should properly be called embolite. The writer 

 was able to discover several spinel twins, which as far as is 

 known have not been previously recognized on this species. 

 With great care several crystals were detached from the lime- 

 stone matrix. These were measured on a two-circle Gold- 

 schmidt goniometer, and drawn by my friend, Professor Yictor 

 Goldschmidt of Heidelberg University, Germany, and I wish 

 to thank him for his kindly assistance in this matter. A top 



Fig. 2. 



Fig. 



-*>» 



Figs. 2 and 3. Spinel twin of Embolite, Veta Eica Mine. Fig. 2 is 

 top view, and fig. 3 is a side view. 



view of one such crystal is shown in fig. 2, and a side view of 

 the same crystal is seen in fig. 3. In addition to the twinning 

 after the spinel law, the following forms were observed : 



Letter 



designation 



of face 



c 



p 



m 



Goldschmidt 

 

 1 

 * 



Miller 

 (001) 



(111) 



(811) 



Naumann 



00 O 00 



o 



303 



Dana 

 i-i 



1 

 3-3 



The cube and octahedron are found in about equal develop- 

 ment. The form m, which is found in but two faces, is that of 

 an icositetrahedron (311,3-3) which has not been previously 

 observed on any minerals of the cerargyrite group as far as the 

 writer is aware. Consequently that form, as w T ell as the twin- 

 ning, seems to be new for embolite. 



