Abstract
Microprobe analyses of 26 natural sapphirines from 17 localities indicate that the predominant chemical substitutions in this mineral occur along the solid solution joinVI(Mg,Fe)2++IVSi4+=VI(Al, Fe)3++IVAl3+. Chromium and manganese are minor substituents. Evidence for the substitution Si⇄Al+1/2Mg+1/2 vacancy is absent within the limits of analytical error.
A partitioning scheme based on electrostatic charge balance considerations has been devised permitting calculation of Fe2+ and Fe3+ from total iron content. Results are in good agreement with previous Mössbauer studies which indicate Fe3+ is sometimes in octahedral and/or tetrahedral coordination.
Distribution coefficients for Fe2+-Mg exchange equilibria between sapphirine-spinel and sapphirine-orthopyroxene are similar for most mineral pairs and suggest that most of the assemblages equilibrated at about the same temperature or that the exchange reactions are insensitive to temperature.
Compositions of synthetic sapphirines as a function of temperature and pressure are qualitatively predictable from crystal chemical considerations. Changes in sapphirine composition along the MgSi= AlAl solid solution join toward more aluminous compositions stabilize the sapphirine structure at high temperatures and low pressures. The limited extent of MgSi=AlAl solid solution observed in natural sapphirines appears to be related to the requirements of geometrical fit among octahedra and tetrahedra in the almost idealized cubic closest-packed anion framework.
Similar content being viewed by others
References
Bancroft, G.M., Burns, R.G., Stone, A.J.: Applications of the Mössbauer effect to silicate mineralogy. II. Iron silicates of unknown and complex structures. Geochim. Cosmochim. Acta32, 547–559 (1968)
Barker, F.: Sapphirine-bearing rock. Val Codera, Italy. Am. Mineral.49, 146–152 (1964)
Bishop, F.C., Newton, R.C.: The composition of low-pressure synthetic sapphirine. J. Geol.83, 511–517 (1975)
Cameron, W.E.: Coexisting sillimanite and mullite. Geol. Mag.113, 497–592 (1976)
Clifford, T.N., McIver, J.R., Stumpfl, E.F.: A sapphirine-cordierite-bronzite-phlogopite paragenesis from Namaqualand, South Africa. Mineral. Mag.40, 347–356 (1975)
Ganguly, J.: Compositional variables and chemical equilibrium in metamorphism. In: Energetics of Geological Processes (S.K. Saxena and S. Battacharji, eds.), pp. 250–284, Berlin, Heidelberg, New York: Springer 1977
Hazen, R.M.: Temperature, pressure and composition: structurally analogous variables. Phys. Chem. Minerals1, 83–94 (1977)
Herd, R.K.: The Petrology of the Sapphirine-Bearing and Associated Rocks of the Fiskenaesset Complex, West Greenland. Ph.D. Thesis, University of London, London, England (1972)
Herd, R.K., Windley, B.F., Chisler, M.: The mode of occurrence and petrogenesis of the sapphirine-bearing and associated rocks of West Greenland. Geol. Surv. Greenland, Report24, 1–44 (1969)
Higgins, J.B.: Crystal Chemistry, Cation Ordering and Polymorphism in Sapphirine. Ph.D. Dissertation, Virginia Polytechnic Institute and State University, Blacksburg, Virginia (1978)
Higgins, J.B., Ribbe, P.H.: Sapphirine II. A neutron and X-ray diffraction study of (Mg-Al)VI and (Si-Al)IV ordering in monoclinic sapphirine. Contrib. Mineral. Petrol.68, 357–368 (1979)
Mason, B., Allen, R.O.: Minor and trace elements in augite, hornblende and pyrope megacrysts from Kakanui, New Zealand, New Zealand J. Geol. Geophys.16, 935–937 (1973)
McKie, D.: Order-disorder in sapphirine. Mineral. Mag.33, 635–645 (1963)
Merlino, S.: Polymorphism in sapphirine. Contrib. Mineral. Petrol.41, 23–29 (1973)
Meyer, H.O.A., Brookins, D.G.: Sapphirine, sillimanite and garnet in granulite xenoliths from Stockdale kimberlite, Kansas. Am. Mineral.61, 1194–1202 (1976)
Moore, P.B.: The crystal structure of sapphirine. Am. Mineral.54, 31–49 (1969)
Saalfeld, H., Jagodzinski, H.: Die Entmischung Al2O3-ubersattigter Mg-Al-Spinelle. Z. Krist.109, 87–109 (1957)
Sahama, Th.G., Lehtinen, M., Rehtijarvi, P., v. Knorring, O.: Properties of sapphirine. Ann. Acad. Sci. Fenn., Series A.III. 1–24 (1974)
Schreyer, W.: Synthetische and naturliche cordierite I. N. Jb. Mineral. Abh.102, 39–67 (1964)
Schreyer, W., Abraham, K.: Peraluminous sapphirine as a metastable reaction product in kyanite-gedrite-talc schist from Sar e Sang, Afghanistan. Mineral. Mag.40, 171–180 (1975)
Seifert, F.: Stability of sapphirine: A study of the aluminous part of the system MgO-Al2O3-SiO2-H2O. J. Geol.82, 197–204 (1974)
Shannon, R.D.: Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides. Acta Cryst.A32, 751–767 (1976)
Taylor, H.C.J.: Melting relations in the system MgO-Al2O3-SiO2 at 15 kb. Geol. Soc. A. Bull.84, 1335–1348 (1973)
Wilson, A.F., Hudson, D.R.: The discovery of beryllium-bearing sapphirine in the granulites of the Musgrave Ranges (Central Australia). Chem. Geol.2, 209–215 (1967)
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Higgins, J.B., Ribbe, P.H. & Herd, R.K. Sapphirine I. Contr. Mineral. and Petrol. 68, 349–356 (1979). https://doi.org/10.1007/BF01164519
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF01164519