296 J. W. Mallet—Stlenide of Bismuth from Guanajuato. 
be found. Possibly, as Rammelsberg had but a very small 
quantity of material on which to work, he may have been led 
to suspect the presence of zinc by a precipitate of aluminum 
hydrate derived from gangue. 
0 evidence, physical or chemical, could be found of the 
presence of pyrite; the trace (unweighable) of iron appears to 
belong to the gangue, 
It is stated that this gangue is galapectite (Halloysite) ; if the 
amount of such mineral present be calculated from the alumina 
the above figures represent the specimen as composed of— 
Guanajuatite 1.220 22. u... 92°17 
Gaasan Halloysite___..__. 6°72 
gee ae 56 
Moisture---_. 18 
99°63 
and the Guanajuatite in the pure state would consist of 
Rrebonetina. 20254. Soe oo 34°33 
Sulphur -. "66 
Re se i ck 65°01 
100°00 
Hence we have the atomic ratio, 
Bi: Se: S= 310: 432; 21, 
or, uniting the sulphur with selenium, 
Bi:Se= 310: 453 = 2:000: 2-922, 
It seems clear that the mineral in question must be viewed 
as sesqui-selenide of bismuth, with isomorphous replacement 
to a variable extent of selenium by sulphur. 
It is also mentioned (this Journal, April, 1867) that Fernan- 
dez has described a second selenide of bisesteh from the same 
locality, and has derived from his analyses of more or less pure 
