Skip to main content

Phonolitic Intrusive Rocks

Gray to greenish-gray sills, laccoliths, and small stocks of phonolite, trachyphonolite, and trachyandesite. Contains phenocrysts of andesine, feldspathoids, aegirine-augite, biotite, and sphene in a finely crystalline plagioclase-biotote-feldsphoid groundmass.
State South Dakota
Name Phonolitic Intrusive Rocks
Geologic age Phanerozoic | Cenozoic | Tertiary | Paleocene Eocene
Primary rock type phonolite
Secondary rock type trachyte
Other rock types
Lithologic constituents
Major
Igneous > Hypabyssal > Felsic-hypabyssal > Hypabyssal-felsic-alkaline (Dike or sill)Phonolite
Igneous > Hypabyssal > Felsic-hypabyssal > Hypabyssal-trachyte (Laccolith)
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
Counties Lawrence