Manganoan Deerite and Calderitic Garnet from High-Pressure Metamorphic Fe-Mn-Rich Quartzites on Andros Island, Greece

Thomas Reinecke
Institut für Angewandte Geophysik, Petrologie und Lagerstättenforschung der Technischen Universität, Straße des 17 Juni 135, EB 310, D-1000 Berlin 12, F.R.G.

Abstract: Calderitic garnet and manganoan deerite have been found in Al-poor, Fe-Mn-rich quartzites associated with metabasic schists on the island of Andros, Cycladic blueschist belt, Greece. Calderitic garnet (30–45 mole % calderite, 55–70 mole % andradite, 0–2 mole % spessartine) occurs in paragenesis with quartz, rhodonite, rhodochrosite, Ni-Mn-bearing magnetite (2–20 mole % trevorite, 6–12 mole % jacobsite, 73–91 mole % Fe3O4), baryte, and orthite. Deerite is associated with quartz, garnet (rich in spessartine, almandine, and andradite), phengite, aegirine, magnetite (containing up to 12 mole % jacobsite), and crossite/riebeckite. Deerite contains 33.0–34.4 wt. % SiO2, 0.53–5.5 wt. % TiO2, 0.09–0.31 wt. % Al2O3, 11.9–33.9 wt. % MnO, 17.5–44.2 wt. % FeOtot, and 1.5–2.8 wt. % MgO. MnO contents correspond to 29–77 cation % Mn2+ per total R2+ cations. Deerites from Andros are thus closer to the hypothetical end-member mangano-deerite, Mn122+Fe63+Si12O40(OH)10, than any other analysis of deerite so far published.

Keywors: deerite • garnet • calderite • Andros • Greece

Mineralogical Magazine; June 1987 v. 51; no. 360; p. 247-251; DOI: 10.1180/minmag.1987.051.360.06
© 1987, The Mineralogical Society
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