Rock unit in Carroll County, GA, is herein named the Oak Grove Gneiss for exposures along Hwy 27 in community of Oak Grove. Unit is described as leucocratic, medium- to coarse-grained, blastoporphyritic biotite-muscovite-plagioclase-quartz-microcline orthogneiss. Microcline megacrysts up to 2 cm are common. Intrudes the Bill Arp Formation at the type locality; elsewhere intrudes the Dog River and Andy Mountain Formations, all of Sandy Springs Group. Is probably a pre- to synmetamorphic pluton and is very similar mineralogically and texturally to the Austell and Sand Hill Gneisses. All three may have been derived from a common parent magma. No dimensions given for the pluton, but geologic map reveals the intrusion to be 1 to 2 km wide and greater than 6 km long.
Source: GNU records (USGS DDS-6; Reston GNULEX).
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