1865.] of some Compounds of Thallium. 557 



Carbonate of Thallium. 



The faces which have been observed are all in one zone, and exhibit a 

 symmetry which is compatible with either the prismatic or the oblique 

 system. The crystals probably belong to the prismatic system. They are 

 aggregated in such a manner as to render it very difficult to isolate a single 

 crystal, or to determine the faces which belong to the different individuals of 

 a group of crystals. 



Observed forms : 1 0, 1 I 0, 2 I 0, 120. Fig. 4. 



1 00, 1 1 51 28 



1 0, 2 1 32 7 



1 0, 1 2 68 57 



1 1 0, 1 1 77 4 



Twins. Twin face 110. One individual is generally united to each of 

 two others, in this respect resembling the twins of cerussite, aragonite, 

 glaserite, and chrysoberyl. 



A cleavage has been observed probably parallel to the faces of the form 

 110; it may, however, be parallel to the faces of the form 100, the com- 

 plexity of the twin crystals being such that it could not be ascertained 

 whether the cleavages observed belonged to one crystal or to two different 

 crystals. 



I am indebted to Mr. Crookes, the discoverer of thallium, for the crystals 

 of nitrate, sulphocyanide, and carbonate of thallium, above described. 



