Day #15 Deskcrop: Labradorite in Ilmenite Ore

We’re back to the Adirondacks to close out this week’s deskcrops. Today’s sample is one of my prized finds. The sample comes from the Tahawus mine dump on the south side of the High Peaks Region, not far from the Mount Marcy trailhead. Large labradorite crystals originating from the Marcy Massif Anorthosite here float in a matrix of magnetite-ilmenite ore. This suggests that the ilmenite-magnetite ore was a liquid phase, presumably immiscible and consanguinous – if not comagmatic – with the parent magma of the labradorite crystals. Elsewhere anorthositic and ferrodioritic dikes crosscut the ilmenite-magnetite orebody.

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Plagioclase Megacrysts in Ilmenite-Magnetite Ore

Upon closer examination of this sample, one can also observe garnet coronas at the contact of the plagioclase and oxide minerals. These little garnet “necklaces” presumably formed during granulite facies regional metamorphism.


Garnet Coronas Surround the Plagioclase Pheno(Xeno?)crysts
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