Annandale Group - Accotink Schist

Accotink Schist (Drake and Lyttle, 1981). Light-gray, yellowish-gray to moderate-brown to very-pale-orange-weathering schist and interbedded with micaceous metagraywacke. Locally, schist contains randomly scattered, discontinuous beds of meta-arenite. Schist intervals are 20 to 210 cm thick, but individual sedimentation units average about 1 cm. Mineralogy: quartz + muscovite + biotite + chlorite + plagioclase; accessory minerals include garnet, magnetite, epidote, apatite, zircon, and pyrite. Micaceous metagraywacke appears to be a more quartzofeldspathic element of a pelitic sedimentary sequence. Unit thickness is unknown because the base is nowhere exposed; the Accotink is intruded by Occoquan Granite.
State Virginia
Name Annandale Group - Accotink Schist
Geologic age Proterozoic Z-Cambrian
Lithologic constituents
Major
Metamorphic > Metasedimentary > Metaclastic > Metasandstone > Metagraywacke
Metamorphic > Schist
Comments Western Piedmont (Northern)
References

Virginia Division of Mineral Resources, 1993, Geologic Map of Virginia: Virginia Division of Mineral Resources, scale 1:500,000.

Virginia Division of Mineral Resources, 2003, Digital Representation of the 1993 Geologic Map of Virginia, Publication 174, CD ROM (ISO-9660) contains image file, expanded explanation in pdf, and ESRI shapefiles, scale 1:500,000.

NGMDB product
Counties Fairfax