Koenig — New Species Melanochalcite and Keioeenaioite. 409 



There are disposable 0-96583 CuO + 0-00506 ZnO, a total of 

 0*97089 molecules of basic oxides. Deducting from this total 

 the requirements of the silico-carbonate, there will be left 

 0-97089— 0-58418 = 0-38671 (CnO,ZnO) to constitute with the 

 water, the hydroxide. But we have 0-42833 molecules of water ; 

 hence there is a surplus of the latter of 0*42833 — 0-38671 = 

 0-03762. This surplus, which amounts to 0-749 per cent, must 

 be declared present as hygroscopic water. It is not determin- 

 able by experiment, since the substance lost at 87 C. — 1-63 

 per cent, and since it is a well-known fact that boiling water 

 converts the hydroxide Cu(H0)2 into the oxide CaO. 



Putting together these figures, we get : 



Copper silico-carbonate 0-8'7627 : copper hydroxide 

 0*77342 = 1-000 : 0-882. 



The formula of melanochalcite is : 



^ Cu,(Si,C)0, •Cu(HO), 



Paragenesis. — In regard to the forming of this mineral sub- 

 stance, one may conceive of at least two modes : 



(1). Cuprite crystallizes first from a solution of copper car- 

 bonate, with the cooperation of a deoxidizing agent, and pro- 

 duces centers or nuclei. At a later period an oxygenated 

 aqueous solution of silicon and carbon tneta-acids invests these 

 nuclei. In presence of an overwhelming basic substratum, the 

 meta condition of the acid changes into the ortho state, and 

 the melanochalcite molecules are formed rapidly, falling out 

 in amorphous aggregates. As the crust increases in thickness 

 the basic substratum's influence decreases and we find mixtures 

 of melanochalcite aggregates with those of chrysocoUa and 

 malachite, because the ortho reverts to the meta state. The 

 complex molecule Cu2(Si,C)0^ is no longer possible ; and, 

 shortly after, we have clear alternating bands of chrysocolla 

 and malachite. 



(2). One can conceive of an aqueous solution holding from 

 the start all the constituents, excepting only oxygen, and from 

 which the least soluble constituents, i. e., CujO, will fall out 

 tirst. But considering the great bulk of the latter compared 

 with that of melanochalcite, chrysocolla and malachite, this 

 view would seem less simple than at first. Both are purely 

 hypothetical ; no experimental facts are known to me outside 

 of the formation of copper sulphides and arsenides. A large field 

 of investigation is open here. The relative absence of native 

 copper in these Arizona cuprite ores is surprising, because these 

 ores are evidently neither metamorphic nor pseudomorphic ; 

 but appear to be automorphic, the same as the native copper 

 ores of Lake Superior. 



