gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1982.045.337.15 An Occurrence of the Spinel End-Member Mg2TiO4 and Related Spinel Solid Solutions Gittins J. Fawcett J. J. Rucklidge J. C. Department of Geology, University of Toronto, Toronto, Canada, M5S 1A1 Brooks C. K. Institute for Petrologi, Kobenhavns Universitet, Øster Voldgade 10, DK-1350, Kobenhavns K. Denmark 1982 45 337 135 137 Copyright © 1982, The Mineralogical Society 1982 Abstract

Black, opaque grains of a spinel whose composition is (Mg2TiO4) 85.8, (MgFe2O4) 0.4 (FeFe2O4) 13.8 (mole %) coexist with a MgAl2O4 spinel and geikielite in a periclase-forsterite marble that has been thermally metamorphosed against an alkalic ultramafic intrusion of Caledonian age in the Kangerdlugssuaq region of East Greenland. The spinel appears to be the closest recorded approach to the end-member Mg2TiO4 among natural rocks, and to be part of a solid-solution series extending across the join Mg2TiO4-MgFe2O4-FeFe2O4, the existence of which has not previously been reported. The composition of the series appears to be controlled by the fO2 that prevails during metamorphism.