2015-CTP-1
Item
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Title
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2015-CTP-1
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Description
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Based off of the association of minerals and textures presented in hand sample and thin section, this rock can be considered a Biotite Gneiss.
Hand sample contains a great majority of biotite crystals with interspersed felsic layer containing more potassium feldspar and quartz. Compositional layering is obvious and is an indicator of metamorphism.
Thin section displays brown, elongate crystals in polarized light which could be hornblende, but due to the Bird's eye texture and measure of the extinction angle of the crystals, we can confirm it is Biotite. In polarized light, there is a curtain surrounding the biotite grains indicating that the crystal is out of equilibrium with the melt. There also appears to be a great amount of clear material, which in cross-polarized light, is revealed as a mix of quartz and feldspar crystals which have lower interference figures.
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Subject
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Metamorphic Petrology
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Creator
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Robert Ashton
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Date
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May 10th, 2015
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Identifier
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2015-CTP-2015
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Mediator
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Tamara Carley
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Rights Holder
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Lafayette College Department of Geology & Environmental Geosciences
