Mafic gneiss (VTY1Y2bmg;0)

Mafic gneiss

Dark-gray to black, fine-grained, magnetite-garnet-hornblende-biotite-diopside-plagioclase gneiss, commonly containing beds of dark-gray vitreous magnetite-garnet quartzite, 2 to 5 cm thick, tremolite-pyroxene gneiss, and biotite-rich, rusty-weathering garnet-quartz schist and gray sulfidic sillimanite quartzite. Occurs as screens within tonalitic gneiss and the Pharaoh Mountain Gneiss and is interpreted as paragneisses older than the tonalitic gneiss (Y2bt). Paragneiss. Rocks of the Adirondacks in Vermont and in the Whitehall, N.Y., area.

State	Vermont
Name	Mafic gneiss
Geologic age	Middle to Early Mesoproterozoic
Lithologic constituents	Major Metamorphic > Metasedimentary > ParagneissDark-gray to black, fine-grained, magnetite-garnet-hornblende-biotite-diopside-plagioclase gneiss; tremolite-pyroxene gneiss. Minor Metamorphic > Schist > Mica-schist > Biotite-schistBiotite-rich, rusty-weathering garnet-quartz schist. Metamorphic > Metasedimentary > Metaclastic > QuartziteDark-gray vitreous magnetite-garnet quartzite; gray sulfidic sillimanite quartzite.
Comments	Original label is Y2bmg, but age is Middle to Early Mesoproterozoic. Changed symbol to Y1Y2bmg.
References	Ratcliffe, N.M., Stanley, R.S., Gale., M.H., Thompson, P.J., and Walsh, G.J., 2011, Bedrock geologic map of Vermont: U.S. Geological Survey Scientific Investigations Map 3184, 3 sheets, scale 1:100,000. https://pubs.er.usgs.gov/publication/sim3184
NGMDB product	NGMDB product page for 96860
Counties	Rutland

Mafic gneiss

Ratcliffe, N.M., Stanley, R.S., Gale., M.H., Thompson, P.J., and Walsh, G.J., 2011, Bedrock geologic map of Vermont: U.S. Geological Survey Scientific Investigations Map 3184, 3 sheets, scale 1:100,000.