The mineralogical characteristics of calcium-iron olivines

Abstract

Summary. :For the estimation of the properties of calcium-iron olivines in ironore sinters, synthetic mixtures of CaO, FeO, and SiO2 were prepared and melle.'t ; the obtained olivines were then examined microscopically and by X-ray powder method. The investigations allowed to state, that with the increase of the basicity of sinters, the relation of Fe : Ca in olivines decreases, which causes the change of their physical, optical, and rSntgenometric properties. THE chemical composition and melting temperatures of calciumiron olivines are presented in the diagrams (CaO-FeO-Si02 and Fe2SiO4-CasSi04) of N. L. Bowen, J. F. Schairer, and E. Posnjak (1932, 1933). From these diagrams it is apparent that calcium-iron olivines form solid solutions with limited solubility. The extreme member fayalite Fe2SiO 4 has a melting temperature 1205 ~ and the extreme member with the highest amount of calcium contains 42 ~o Fe2Si04 and 59 % CazSiO 4 by weight. Calcium-iron olivines are the chief component of the silicate phase in iron-ore sinters, strongly influencing the reducibility and strength of self-fluxing sinters. Synthesis. The varying chemical composition of olivines in iron-oresinters necessitated an investigation of the mineralogical characteristics of calcium-iron olivines. Therefore a number of syntheses of olivines were carried out at a temperature above the melting point, using pure components CaO, FeO, and Si02; FeO was obtained by the dissociation in vacuum of ferrous oxalate, Fe(C~Oa). 2HsO. The samples were melted in pots made of armco-iron in vacuum or in argon. The assumed and actually obtained analyses of synthetic olivines are presented in table I. From the figures in this table it is apparent that the passing of some FeO into FeaO 4 could not be avoided. The presence of FeaO a has been confirmed by microscopic examination; Bowen, Schairer, and Posnjak found 2"0 to 2"8 ~o Fe20s in their silicate melts.Optical properties of synthetic calcium-iron olivines. These olivines are characterized by a dark eolour, from dark green or brown for fayalite

Iron ore sinter in the analytical transmission electron microscope

“…Bowen suggests that the Fe-olivine, FezSiO4, is capable of accepting a greater range of Ca for Fe replacement up to a limit corresponding to approximately Cal.zFe0. s SiO4 (later confirmed by Wyderko and Mazanek, 1968). This limit of Ca in the olivine structure does not extend into the range of Ca-Fe silicates found in this study.…”

Decadal‐scale variations in geomagnetic field intensity from ancientCypriot slag mounds

“…Although there is a solid solution between fayalite and kirschsteinite, occurrences of the latter are rare in nature and are typically restricted to Ca‐Fe‐rich silicate melts that are silica‐undersaturated and allowed to cool in low‐pressure conditions. This is exactly the environment that exists for most metallurgical slags, where kirschsteinite can be common [ Wyderko and Mazanek , ]. Olivine grains generally occur as large skeletal laths that confine the sizes and shapes of other minerals in the slag, an indication that they nucleated from the melt first and grew fastest (Figures a, c, f).…”

Ancient Metallurgical Iron Slags—Chemical, Powder X-ray Diffraction and Mössbauer Spectroscopic Study

“…116-1, 131-1, and 131-2 also correspond to the practically identical occupancy of the M2 position with Fe 2+ (Table 3). The calcium isomorphism in fayalite is also confirmed by the shift of the X-ray [130] reflection-from 1.80Å to 1.84Å [26] (Figure 2). Mn 2+ and Mg 2+ can also be included in the M2 position [25].…”