abstracts: geochemistry 329 



In addition to the oxides whose siisceptibiht}' depends upon their 

 content of FeO, there exists also a highly ferromagnetic form of Fe203, 

 which appeal's to be rare in natural occurrence. 



The natural iron-oxide minerals are similar to the artificial in that 

 many are solid solutions of Fe304 in Fe203. Others are mixtures of 

 Fe304 and Fe203. If the ferrous iron is not in solid solution or in mag- 

 netite admixture, the magnetic susceptibility falls below the norma'. 



Some natural oxides can be magnetically fractionated; and the less 

 magnetic portions are found to deviate more widely from normal 

 than the more magnetic. The cause of this deviation is not yet en- 

 tirely clear. 



Martite is a pseudomorph after magnetite, but its constituent gran- 

 ules or fibers consist usually of a solid solution of Fe304 in Fe203. The 

 ferrous iron content and the magnetic susceptibility of the specimens 

 examined suggest that they have been produced at temperatures con- 

 siderably higher that atmospheric. 



R. B. S. 



GEOCHEMISTRY. — Zonal growth in hematite, and its hearing on the 

 origin of certain iron ores. R. B. Sosman and J. C. Hostetter. 

 Bull. Amer. Inst. Min. Eng. 933-943. June, 1917. 

 The powdered oxide from certain crystals of hematite from Elba 

 contains considerable FeO and can also be fractionated magnetically. 

 It is therefore not homogeneous, as would be the case if the crystal were 

 a uniform solid solution throughout. Analyses and magnetic measure- 

 ments on a cross-section of an Elba crystal showed that the magnetic 

 susceptibility' and percentage of FeO vary, not irregularly, but con- 

 tinuously, being highest at the base and lowest at the free-growing 

 tip of the crystal. The crystal is therefore zoned with respect to its 

 FeO content. * 



Since Fe304 goes into solid solution in Fe203, forming a single solid 

 phase of var3dng composition and properties, a zonal distribution of 

 FeO is to be expected in an oxide of iron depositing from a vapor or 

 solution. The occurrence of such zonal growth indicates continuously 

 changing conditions of temperature, pressure, and concentration during 

 the formation of the crystals. Several ore deposits of contact-meta- 

 morphic origin show a zonal distribution of ferrous iron, probably 

 arising from the sanie causes as the zoning of the single crystals. 



R. B. S. 



