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Trachytic Intrusive Rocks

Tan to reddish-brown, iron-stained stocks, laccoliths, sills, and dikes of trachyte, quartz trachyte, and alkalic rhyolite. Contains phenocrysts of sanidine, orrthoclase, anorthoclase, aegirine-augite and biotite in a finely crystalline orthoclase-quartz biotite groundmass.
StateSouth Dakota
NameTrachytic Intrusive Rocks
Geologic agePhanerozoic | Cenozoic | Tertiary | Paleocene Eocene
Original map labelTt
Primary rock typetrachyte
Secondary rock typetrachyte
Other rock typesrhyolite
Lithologic constituents
Major
Igneous > Hypabyssal > Felsic-hypabyssal > Hypabyssal-rhyolite (Dike or sill)
Igneous > Hypabyssal > Felsic-hypabyssal > Hypabyssal-quartz-trachyte (Laccolith)
Igneous > Hypabyssal > Felsic-hypabyssal > Hypabyssal-trachyte (Stock or pipe)
Map references
Martin, J. E., Sawyer, J. F., Fahrenbach, M. D., Tomhave, D. W., and Schulz, L. D., 2004, Geologic Map of South Dakota: South Dakota Geological Survey
Unit references
Martin, J. E., Sawyer, J. F., Fahrenbach, M. D., Tomhave, D. W., and Schulz, L. D., 2004, Geologic Map of South Dakota: South Dakota Geological Survey
Geographic coverageLawrence - Meade

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