1850.] On Calderite, a new Rock from Burdwan, 147 



Via Humida. 



From the solution in hydrochloric acid, which acts readily on the 

 pulverised mineral, a strong arsenical odour is evolved, but both from 

 this and from the nitro-hydrochloric solution only traces of arsenic 

 can be obtained, amounting at most to 0.15 or 0.20 per cent. The 

 siliceous residuum is remarkably tenacious, adhering strongly to the 

 bottom of the capsule, unless frequently stirred, and even then leaving 

 a thin coating, only to be removed by caustic Potass, and slightly cor- 

 roding the glass. 



The constituent parts of a fair average of the mineral I find to be — 



Or per centage if of man= 

 ganese and iron only. 



Silex, 46.35 



Alumina, 0.35 



Lime, 1 .00 



Arsenic, 0.20 



Perox.-Iron, 30.18 58.64 



Protox. Manganese, 21.00 41.36 



99.08 100.00 



Loss, partly fluorine, of which there 



are traces, .92 



100.00 

 The most compact and apparently homogeneous specimens of this 

 rock are distinctly seen upon closer inspection to be mere aggregates of 

 a black (or very dark greenish black) mineral, and transparent granules 

 and fragments of quartz, in addition to the golden resinous coating 

 mentioned before. Now if the constituent parts of any specimen can 

 be seen, the specimen is then clearly a rock and not a mineral ; and I 

 have therefore classed this new specimen as a rock without reference 

 to the abundance or scarcity of it. It is evident also that we must set 

 aside all rules of nomenclature to call it a silicate of iron and manganese 

 for the amount of silica will probably differ in every analysis, and we 

 know not if the greenish black part contains any or how much silica in 

 its composition, and that it may be a simple compound of the oxides 

 only. 



u 2 



