ABSTKACTS: MINEEALOGY 95 



a low-acid field where only sphalerite is obtained, and an intermediate 

 field where mixtures of the two are obtained. 



No crystalline zinc sulphide could be obtained from the hydrochloric- 

 acid solutions, but the iron disulphides were crystallized from them, 

 and always contained much more marcasite for an equivalent quantity 

 of acid, i.e., hydrochloric acid has a much greater influence on the crystal 

 form than an equivalent quantity of sulphuric acid, which should be the 

 ease if the hydrogen ion concentration were the real determining factor. 



The acid concentration required to give rise to pure marcasite or 

 pure wurtzite falls with the temperature and is close to neutrality for 

 marcasite at ordinary temperature, and probably so for wurtzite. 



Several conditions other than acidity and temperature were varied 

 in the formation of wurtzite, where the process was necessarily more 

 complicated; these were zinc concentration, addition of sodium sulphate 

 to the solutions, and hydrogen-sulphide pressure. None of these had 

 any influence, except as they affected the acidity. 



At temperatures of 25° and 200°C. from sulphuric-acid solutions and at 

 300°C. from hydrochloric-acid solutions we obtained a product containing 

 95 per cent of marcasite comparable with the purest natural marcasite we 

 have had in our hands. Since this determination depends on the quan- 

 tity of iron dissolved from the mineral under definite conditions, and 

 different natural specimens vary somewhat, it may be that this product 

 is pure synthetic marcasite. 



Some new data on the genesis of the natural minerals are cited. 



E. T. A. 



MINERALOGY. — The siumltaneous crystallization of calcite and certain 

 sulphides of iron, copper, and zinc. A crystallographic study. H. 

 E. Merwin. Am. Jour. Sci. (4), 38: 355-359. 1914. 

 The study of three occurrences of the sulphides of iron and zinc has 

 established with certainty the deposition of marcasite, and with strong 

 probability the deposition of wurtzite contemporaneously with calcite. 

 The marcasite is definitely oriented with regard to the calcite and also 

 the accompanying pyrite. A close similarity between the crystallo- 

 graphic elements of pyrite and marcasite is shown. H. E. M. 



MINERALOGY. — The optical properties of roscoelite. Fred. E. 

 Wright. Am. Jour. Sci. (4), 38: 305-308. 1914. 

 The optical data were obtained on unusually good material, kindly 

 loaned by Dr. W. F. Hillebrand for the purpose. Color, olive green. 



