On Emerald Nickel from Texas. 81 



existence of carbonic acid in this mineral, by a notice from 

 Dr D. R. Thomson,* describing as a new mineral a carbonate 

 of nickel from the United States, coating specimens of chro- 

 mic iron. Professor Shepard also mentioned to me that he 

 had found carbonic acid in the Texas nickel mineral, first 

 described by me. I have, therefore, made a new analysis of 

 the mineral in question, selecting the finest and most trans- 

 parent coloured specimens in my power. 



The following mineralogical description is mainly the same 

 which I have before given, save that having much better 

 specimens on which to determine the specific gravity, that 

 now given may be regarded as more correct than the former 

 determination : — 



Emerald Nickel. 



Massive, stalactitic, occurring in thin crusts on chromic 

 iron. Hardness = 3 — 3*26, being but little above calc-spar. 

 Specific Gravity = 2-570 — 2*693, two trials on different por- 

 tions. Lustre, vitreous, brilliant. Colour, emerald-green. 

 Transparent. Streak, delicate pea-green. Very brittle. Its 

 pyrognostic characters have already been so fully described 

 in the article first quoted, that it is useless to repeat them 

 here ; they differ in no respect from those of pure, artificial 

 hydrate of nickel. 



The water of this mineral is partially expelled at the ordi- 

 nary temperature of a water-bath (212° F.) ; this fact led to 

 estimating the total volatile product of the mineral too low, 

 in the former description of this species. Carefully dried over 

 sulphuric acid, the mineral lost, on two trials, 41*370 and 

 41*008 ; mean = 41*189 per cent. 



The carbonic acid was estimated in the apparatus described 

 by Fresenius and Will for analysing carbonates. 



The mean of the three trials gave 11*691 of C 0^. A trace 

 of magnesia in the specimen examined was disregarded, as 

 being accidental. The mineral rests on a basis of carbonate 

 of magnesia, which is difficult to separate entirely. 



The constitution resulting from the analysis 



* Phil. Mag., Dec. 1847, p. 641. 

 VOL. XLVI. NO. XCI. — JAN. 1849. 



