Packsaddle Schist

Packsaddle Schist
State Texas
Name Packsaddle Schist
Geologic age preCambrian (Proterozoic); Llano Series
Lithologic constituents
Major
Metamorphic > Schist (Amphibolite)Dominantly dark basic rocks including biotite, amphibolite, and graphitic schists and crystalline limestone also light-colored feldspathic bands resembling quartzite. Mostly feldspathic amphibole and biotite schist, predominantly dark colored. A sample described by Barnes composed of anthophyllite, plagioclase, and biotite. Opaque minerals include apatite, zircon, garnet, and staurolite?.
Comments Comstock and Dumble (1890) included unit in the Packsaddle series, described as metamorphosed shaly beds and marble (near base) forming top div. of Texan system. Barnes (1952) described the unit as mostly feldspathic amphibole and biotite schist and chiefly dark colored. (from Llano Sheet, Geol. Atlas of Texas) From top down: Click Fm.-mostly hornblende schist, underlain by leptite and qtz-feldspar-mica schist which grades into hornblende schist SE; thickness ca. 7,800 ft. Rough Rider Fm.-gray leptite, qtz-feldspar-mica schist, and biotite-cordierite gneiss local muscovite schist, biotite schist, and biotite-microcline gneiss; thickness ca. 5,200 ft. Sandy Fm.-alternating units of hornblende schist, and quartz-feldsparpmica schist and leptite; thickness ca.2,100 ft. Honey Fm.-upper part graphite schist, hornblende schist, and marble with graphite schist interbeds; middle part-muscovite schist, changes to leptite,graphite, schist, and hornblende schist toward SE, one prominent marble; lower part-hornblende schist, graphite schist, leptite, and marble; thickness ca 7,800 ft.
Stratigraphic units from top down, Click Formation, Rough Ridge Formation, Sandy Formation, and Honey Formation
References

Barnes, V.E., Romberg, F., and Anderson, W.A., 1954, 19th International Geologic Congress, Algiers 1952, Comptes rendus, sec. 9, pt. 9, p. 152-153.

Wilmarth, M.G., 1938, Lexicon of geologic names of the United States: U.S. Geological Survey Bulletin 896, 2396 p.

https://pubs.er.usgs.gov/publication/b896

Comstock, T.B., and Dumble, E.T., 1890, (title unknown) Texas Geol. Survey 1st annual report pl. 3 p. lvii, lviii, 276-281.

Paige, S., 1912a, Llano-Burnet, Texas: U.S. Geological Survey, Geologic Atlas of the United States, Folio 183.

https://pubs.er.usgs.gov/publication/gf183

Barnes, V.E., 1952, Hilltop quadrangle, Gillespie, Llano, and Mason Counties, Texas: Geologic Quadrangle Maps, Bureau of Economic Geology, The University of Texas, Austin, Texas, scale 1:31,680.

Mutis-Duplat, Emilio, 1982, Geology of the Purdy Hill quadrangle, Mason County, Texas: Bureau of Economic Geology, the University of Texas at Austin, Geologic Quadrangle Map 52, scale 1:24.000.

Bureau of Economic Geology, 1992, Geologic Map of Texas: University of Texas at Austin, Virgil E. Barnes, project supervisor, Hartmann, B.M. and Scranton, D.F., cartography, scale 1:500,000.

Bureau of Economic Geology, 1992, Geologic Map of Texas: University of Texas at Austin, Virgil E. Barnes, project supervisor, Hartmann, B.M. and Scranton, D.F., cartography, scale 1:500,000.

NGMDB product
Counties Blanco - Burnet - Gillespie - Llano - McCulloch - Mason - San Saba