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Some of the relations of magnetite and hematite

1919; Volume: 14; Issue: 5 Linguagem: Inglês

10.2113/gsecongeo.14.5.353

1554-0774

Thomas Monteith Broderick,

Minerals Flotation and Separation Techniques

With the excepti,on o.f the titaniferous magnetites, comparatively little work has been done on polished surfaces of the iron ores.Lack of interest in them has .beendue chiefly to the fact that comparatively few points of economic importance which could have 'been settled.bysuch examination have arisen.This, added to l•he difficulty of properly polishing them, and the necessity of having equipment which will furnish powerful illumination for examination at high magnifications, accounts for the investigators' preference to ores of other metals.Examination of some forty polished sections of magnetitehematite ores from 'widely scattered localities serves to suggest a series of problems concerning which little is known.The writer realizes that this article touches upon many points without presenting definite conclusions, but it is thought that the relationships observed are worthy of description. TI-IE EVIDENCE OF SOLID SOLUTION IN THE SERIES Fe2Oa--FeaO4.One of the first things to be considered in the study of the relations of magnetite and hematite is the evidence of the exist-• Communication from the Laboratory of Economic Geology of Massachusetts Institute of Technology, Cambrid,ge, Mass.353 3 54 T. M. BRODERICK.ence of solid solutions intermediate in composition.Several articles have appeared recently, in which the. conclusion is reached that solid solutions in the system Fe2Oa--FeaO4 exist in nature?The following quotations illustrate the confidence of the writers: "Natural oxides of iron intermediate in composition between Fe20, and Fe80, are much more common than is generally supposed."a "'l•hese martites are found in fact to be both pseudomorph and solid solution at the same time."4 "The natural iron oxide minerals are similar to the artificial in being in many cases solid solution of Fe80, in Fe.•O•."5 "Some of these (natural) oxides are true homogeneous solid solutions."6 The writers of these articles admit that two explanations would account for the presence of FeO in the specimens which they examined.It could be pres.enteither in solid solution in the hematite or in adm.ixed magnetite (assuming no ferrous silicate or carbonate present).The evidence upon which the former alternative was chosen is based upon (I) the apparent microscopic and magnetic homogeneity of the material and (2) in the case of certain ores, notably th'at from Juragua, Cuba, an apparent peculiarity in their magnetic behavior.In regard to the microscopic homo.geneity of the specimens examined at the Geophysical La. boratory, the writer can find in the descriptions.of the methods of research no evidence of any microscopic examination of polished surfaces having been made.In addition to many other iron ores, the writer has examined polished• surfaces of ores from the localities which are considered 'by Sosman and Hostetter as .being the best examples o.f solid solution.In the cases of the ores from• Daiquiri and Juragna, the writer was, fortunate enough to secure the same