TELLURIUM IN NEW SOUTH WALES ORES. 119 



The hardness is aljout 3, but appears to vary considerably in 

 the ditfereut specimens, as calcite will just so'atch some but is 

 itself scratched by others. 



From the roughly cubical shape of this mineral taken in con- 

 junction with the existence of numerous cubical cavities, like 

 those left after the decomposition of iron pyrites, in the telluri- 

 bismuthic ochre and gossan, it appeal's to me highly probable 

 that this variety of montanite is pseudomorphous after iron 

 pyrites, and the analysis proves that the dark brownish red 

 colour is due to the combination of iron with the montanite. 



It may therefoi'e be described provisionally as a ferruginous 

 variety of montanite, pseudomorphous after iron pyrites." 



On analysis the tetradymite (or bismuth telluride) Bi^ Tcg also 

 as Bi^ Te, S gave the following composition : — 



Metallic Bismuth ... ... 59-66 



Tellurium 33-16 



Selenium ... ... ... ... nil 



Sulphur ... ... ... ... 4-54 



Iron -42)^ 



Silica •40/ 



98-18 

 The above analysis corresponds with the formula given for the 

 compound containing sulphur — Bij Te.^ S. 



The sp. gr. of the mineral is 7-381. 



Before the blowpipe the mineral easily melted, coating the 

 charcoal with a yellow and white incrustation, also giving a green 

 colour to the outer flame. No selenium smell observed. Soluble 

 in nitric and sulphuric acids. 



It was found that some of the tellurium alloyed with the 

 bismuth on fusion with potassium cyanide, the slag giving a rich 

 purple coloured solution, which deposited the element on standing 

 as a black metallic powder, the solution losing its colour. 



This reaction obtained by me in the first case on testing the 

 minerals, was the cause of my suspecting the presence of a 

 considerable quantity of tellurium. 



Telluric-bismuth, tetradymite, or bornite is stated to have 

 been found in Virginia, Georgia, North Carolina, Cumberland, 

 and Brazil often coated with montanite Bi^, O,, TeO^ -I- H, O (or 

 2 H., O) bismuth-tellurate — formed through the oxydation of 

 the tetradymite, and is in reality a pseudomoi'ph after the 

 latter on which it forms a coating. The tellurium is sometimes 

 replaced by sulphur and selenium. The sp. gr.is given at 7-2 to 

 7-9. Hardness 1 to 2. 



♦These two elements are no doubt impurities, it being found difficult to detach the 

 mineral from the matrix. 



