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A general equation for estimating Fe3+ concentrations in ferromagnesian silicates and oxides from microprobe analyses, using stoichiometric criteria

  • G. T. R. Droop (a1)
Abstract

A simple general equation is presented for estimating the Fe3+ concentrations in ferromagnesian oxide and silicate minerals from microprobe analyses. The equation has been derived using stoichiometric criteria assuming that iron is the only element present with variable valency and that oxygen is the only anion. In general, the number of Fe3+ ions per X oxygens in the mineral formula, F, is given by;

where T is the ideal number of cations per formula unit, and S is the observed cation total per X oxygens calculated assuming all iron to be Fe2+. Minerals for which this equation is appropriate include pyralspite and ugrandite garnet, aluminate spinel, magnetite, pyroxene, sapphirine and ilmenite. The equation cannot be used for minerals with cation vacancies (e.g. micas, maghemite) unless, as in the case of amphiboles, the number of ions of a subset of elements in the formula can be fixed. Variants of the above equation are presented for some of the numerous published schemes for the recalculation of amphibole formulae. The equation is also inappropriate for minerals showing Si4+ = 4H+ substitution (e.g. staurolite, hydrogarnet), minerals containing an unknown proportion of an unanalysed element other than oxygen (e.g. boron-bearing kornerupine) and minerals containing two or more elements with variable valency.

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References
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Anderson, A.T. (1968) Oxidation of the La Blache Lake titaniferous magnetite deposit, Quebec. J. Geol. 76, 528-47.
Brown, E.H., and Bradshaw, J.Y. (1979) Phase relations of pyroxene and amphibole in greenstone, blueschist and eclogite of the Franciscan Complex, California. Contrib. Mineral. Petrol. 71, 67-84.
Carmichael, I.S.E. (1967) The iron-titanium oxides of salic volcanic rocks and their associated ferromagnesian silicates. Ibid. 14, 36-64.
Carpenter, M.A. (1979) Omphacites from Greece, Turkey and Guatemala: composition limits of cation ordering. Am. Mineral. 64, 102-8.
Cawthorn, R.G., and Collerson, K.D. (1974) The recalculation of pyroxene end-member parameters and the estimation of ferrous and ferric iron content from electron microprobe analyses. Ibid. 59, 1203-8.
Essene, E.J., and Fyfe, W.S. (1967) Omphacite in Californian metamorphic rocks. Contrib. Mineral. Petrol. 15, 123.
Higgins, J.B., Ribbe, P.H., and Herd, R.K. (1979) Sapphirine. I: Crystal chemical contributions. Ibid. 68, 349-56.
Lindsley, D.A. (1983) Pyroxene thermometry. Am. Mineral. 68, 477-93.
Meagher, E.P. (1982) Silicate garnets. In Reviews in Mineralogy,5 0rthosilicates(P. H. Ribbe, ed.) 25-66. Mineral. Soc. America.
Papike, J.J., Cameron, K.L., and Baldwin, K. (1974) Amphiboles and pyroxenes: characterisation of other than quadrilateral components and estimates of ferric iron from microprobe data. G.S.A. Abstracts with Programs, 6,1035-5. (abs.)
Richardson, S.W. (1968) Staurolite stability in a part of the system Fe A1 Si-O-H. J. Petrol. 9, 467-88.
Rick wood, P.C. (1968) On recasting analyses of garnet into end-member molecules. Contrib. Mineral. Petrol. 18, 17598.
Robinson, P. (1980) The composition space of terrestrial pyroxenes—-internal and external limits. In Reviews in Mineralogy, 7 Pyroxenes(C. T. Prewitt, ed.) 419-94. Mineral. Soc. America.
Spear, F.S., Schumacher, J.C., Laird, J., Klein, C., Evans, B.W., and Doolan, B.L. (1982) Phase relations of metamorphic amphiboles: natural occurrence and theory. Ibid. 9B Amphiboles: Petrology and experimental phase relations(D. R. Veblen and P. H. Ribbe, eds.) 1-227.
Stout, J.H. (1972) Phase petrology and mineral chemistry of coexisting amphiboles from Telemark, Norway. J. Petrol. 13, 99-145.
White, A.J.R. (1964) Clinopyroxenes from eclogites and basic granulites. Am. Mineral. 49, 883-8.
Yoder, H.S. and Tilley, C.E. (1962) Origin of basalt magmas: an experimental study of natural and synthetic rock systems. J. Petrol. 3, 342-532.
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Mineralogical Magazine
  • ISSN: 0026-461X
  • EISSN: 1471-8022
  • URL: /core/journals/mineralogical-magazine
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