MINERALOGY. b*93 



CHEMICAL MINERALOGY. 



Some interesting contributions have been made to the important part 

 of chemical mineralogy dealing with the artificial formation of minerals. 

 An extended paper by Doelter, of Graz, describes the formation of a 

 number of sulphides, as galena, cinnabar, chalcocite, bornite, covellite, 

 chalcopyrite, and pyrite, and also the sulphantimonites, miargyrite, 

 jamesonite, and bournonite. The special object of the investigation was 

 to accomplish the end aimed at under conditions and by methods as 

 similar as possible to those that nature may be supposed to have em- 

 ployed; in other words, to avoid for the most part very high tempera- 

 tures and the use of reagents that can hardly have entered into na- 

 ture's processes. For example, it was shown that pyrite may be pro- 

 duced without essential elevation of temperature, by the action of water 

 containing hydrogen sulphide upon hematite (FcaOs), as also upon siderite 

 (FeCOs) and magnetite (Fe304). Similarly the experiments with galena 

 lead to the conclusion that it could be produced in nature by hydrogen 

 sulphide acting upon solutions of lead carbonate and lead chloride. 

 Cubes of galena were formed in a tube containing lead chloride, hydro- 

 gen sulphide, and bicarbonate of soda, kept for five months at the ordi- 

 nary temperature of the laboratory. Cinnabar was obtained in minute 

 brilliant red crystals by digesting mercury in a sealed tube contain- 

 ing hydrogen sulphide for six days at a temperature of 70° to 9(P C. 

 Covellite (CuS) was produced from malachite in a sealed tube contain- 

 ing a hydrogen sulphide solution at 80° to 90°. Further, the same re- 

 sult was obtained by treating cupric oxide (CuO) with the gas (H2S) 

 in a glass tube at about 200° ; at a higher temj^erature 250° to 400° chal- 

 cocite (CU2S) was formed. The other experiments were of a similar 

 nature. 



Wells and Penfield, in connection with their investigation of the new 

 mineral, gerhardtite (see a later page), were led to study the formation 

 and characters of an artificial basic cupric nitrate, having the same 

 composition with it, viz, 4CuO, N2O5, 3H2O. The normal nitrate was 

 heated with metallic coj)per in a sealed tube to about 150° C. for a day or 

 more, the result being the formation of crystals of the compound named. 

 These were tabular in habit, monoclinic in crystallization, but in di- 

 mensions, as, too, in optical properties, remarkably near the ortho- 

 rhombic gerhardtite. The axial ratios, for example, are : 



Gerhardtite a : b : (5=0-9218 : 1 : 1-1562, /3=90o 



Artilicial compound a : b : 6=0-9178 : 1 : 1 4102, /?-^850 27 



Moreover, the cleavage corresponds, as also the plane of the optic 

 axes ; the dispersion, double refraction, and pleochroism also are simi- 

 lar. The same artificial compound, first correctly established by Ger- 

 hardt, was also made by Wells by adding sodium acetate to a hot di- 

 lute solution of cupric nitrate, boiling, then washing the precipitate in 

 cold water; it consisted of minute crystals, having the same composition 

 as that given. 



