Since we seem to be getting fairly comprehensive, let me add an
additional type of corundum occurrence that is similar to one that
Eric mentioned. We have found aluminous enclaves in coarse gedrite
gneiss from Orijarvi (Finland) that contain an outer rind of
cordierite with an interior containing corundum-magnetite
symplectites, Al-spinel and hogbomite. The hogbomite is in large
well-formed crystals suggesting it may be a primary constituent of
these enclaves and not a secondary reaction of spinel. John
Schumacher has described similar enclaves from orthoamphibole
gneisses from New England - his also contained sapphirine, in
addition to the other phases I noted. (Ref: Schneiderman and Tracy,
1991, American Mineralogist 76, 942-955).
Bob T.
>Dear all,
>
>just to give a different example:
>Corundum may also form by metamorphic reactions at high T in low-silica
>sub-domains of felsic granulites. We have found corundum in hercynite +
>cordierite pseudomorphs after kyanite (Fig. 2d of Marschall et al.,
>2003). The rocks were also partially melted during their HT history,
>but formation of corundum is clearly not related to melting or melt
>crystallisation.
>
>cheers,
>
>horst
>
>
>Marschall HR, Kalt A, Hanel M (2003) P-T Evolution of a Variscan Lower
>Crustal Segment: a study of granulites from the Schwarzwald, Germany. J
>Petrol 44: 227-253
>
>
>--
>Horst R. Marschall
>Mineralogisches Institut
>Universitaet Heidelberg
>INF 236
>69120 Heidelberg
>Germany
--
Robert J. Tracy
Professor of Geosciences
5064 Derring Hall
Virginia Tech
Blacksburg VA 24061-0420
Ph: 540-231-5980
Fax: 540-231-3386
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