Trachytic Intrusive Rocks (SDTt;0)

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.

State	South Dakota
Name	Trachytic Intrusive Rocks
Geologic age	Eocene to Paleocene
Lithologic constituents	Major Igneous > Hypabyssal > Felsic-hypabyssal > Hypabyssal-trachyte (Stock or pipe, Dike or sill, Laccolith) Igneous > Hypabyssal > Felsic-hypabyssal > Hypabyssal-quartz-trachyte (Stock or pipe, Dike or sill, Laccolith) Igneous > Hypabyssal > Felsic-hypabyssal > Hypabyssal-rhyolite (Stock or pipe, Dike or sill, Laccolith)
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, GM 10, scale 1:500,000.
NGMDB product	NGMDB product page for 72317
Counties	Lawrence - Meade

Trachytic Intrusive Rocks

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, GM 10, scale 1:500,000.