R1825 - Diorite
Item
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Title
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R1825 - Diorite
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Description
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Diorite
Location: Near Azusa, Los Angeles County, California
Geologic Age: Cretaceous
Megascopic Description: A dark gray medium grained somewhat gniessoid rock consisting of black hornblende, glassy plagioclase, with occasional yellow/brown grains or sphene.
Microscopic Description: Green hornblende, the dominant species contributes to a moderately well-developed gniessoid foliation in the subparallel subhedra, partly replaced by Biotite, in both anhedral and patches and euhedral tablets. The medium plagioclase in anhedral, slightly zoned gradationally and locally has central parts sericitized. Large sphene euhedra form a conspicuous accessory. Others are Epidote, rare allanite, apatite, and magnetite
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