Pegmatite intrusion in Baltimore gneiss in roadcut

Pegmatite intrusion in Baltimore gneiss in roadcut

Intrusions (Geology)

Pegmatite intrusion in Baltimore gneiss in roadcut, east bank of Schuylkill River, south of Spring Mill

Ashley, Geo. H. (George Hall), 1866-1951

1935-05-31

Montgomery

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Photographs

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5524

A thin section of the intrusive rock shows the chief mineral to be microcline with granulated borders, and some interstitial quartz. Albite is present, both as separate grains, in part sericitized, and in perthitic intergrowth with microcline. Both muscovite and biotite are present, the latter being in part altered to chlorite. Accessories are apatite, zircon, epidote, and magnetite. The micas, feldspars and quartz, with the possible accessory of the coarser vein quartz have been cataclastically deformed.

321.1

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Pennsylvania Geological Survey

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