94 abstracts: mineralogy 



by sulphur in the case of pyrite; in other words, that more of the sul- 

 phur in pyrite is oxidized. Stokes considered only the relation of />, 

 the percentage of sulphur oxidized, to y, the percentage of pyrite in the 

 sulphide mixture. We have shown that this curve is a hyperbola. 

 This characteristic behavior of pyrite and marcasite towards oxidizing 

 agents is probably general. It has been found by other observers that 

 nitric acid and hydrogen peroxide both oxidize more of the sulphur in 

 pyrite under the same conditions. 



E. T. A. 



MINERALOGY. — -Effect of tem'perature and acidity in the formation of 

 marcasite {FeS^) and wurtzite (ZnS); a contribution to the genesis of 

 unstable forms. E. T. Allen and J. L. Crenshaw. Microscopic 

 study by H. E. Merwin. Am. Jour. Sci. (4), 38: 393-431. 1914. 

 Our former results on the genesis of marcasite and wurtzite have 

 been reinvestigated, the former conclusions have been confirmed, and 

 new data determined. The specific influence of acidity and alkalinity 

 on the crystal form of the sulphides investigated has been much more 

 rigorously demonstrated. Only from acid solutions were the unstable 

 forms obtained. The sulphides were prepared by the action of hydro- 

 gen sulphide on acidic solutions of zinc salts and by hydrogen sulphide 

 and sulphur on acidic solutions of ferrous salts. The unstable forms 

 were usually mixed with the corresponding stable forms, viz., sphalerite 

 and pyrite, and the composition of the mixtures was determined, ap- 

 proximately for the zinc sulphides, by microscopic estimation; and with- 

 in 1 to 2 per cent by the Stokes method for the iron disulphides. 



As previously found, the higher the maximum temperature of experi- 

 ment, other conditions remaining unchanged, the greater the quantity 

 of the stable form, pyrite or sphalerite, obtained in the product. 



As previously concluded, the higher the percentage of acid in the 

 solution, other conditions remaining unchanged, the greater in general 

 the quantity of the unstable sulphide, marcasite or wurtzite. The re- 

 lation between the percentage of marcasite and the average acidity was 

 practically linear for maximum temperatures of 200° and 300°C. There 

 are also indications of a similar relation in the case of wurtzite. In the 

 case of wurtzite, however, the final acid was found to be the 'determining 

 factor, since at 300° and 325°C. wurtzite appears to change into sphal- 

 erite when heated with sufficiently dilute acid. The temperature-acid 

 field in the case of zinc salts may be divided by two boundary curves 

 into three subfields : a high-acid field in which only wurtzite is obtained, 



