The St. Clair Limestone is a geologic unit in
Arkansas, and Oklahoma. It is classified as a Geologic Member in Indiana and Missouri. It dates back to the Middle of
Silurianperiod. It is high density, high magnesium dolomitic limestone.[2] It was originally classified as a marble in Oklahoma due to the fact that it would hold a high polish, hence
Marble City. It is sold in slabs and as tiles, in a similar manner as marble would be.[3] This unit has many economic uses in Arkansas and Oklahoma. It is used as a construction material, manufacture of
quicklime, and manganese deposits are mined as well.[4] The St Clair is designated as a member of the
Bainbridge Group in the State of
Indiana.[5] In
Illinois,
Missouri,
Arkansas and
Oklahoma it is part of the
Hunton Megagroup. The St. Clair is the Basal member of the
Niagaran Series, making it part of the
Tippecanoe sequence. Throughout most of the Southern extent the unit is roughly 10 to 20' thick. Moving northward it thickens to approximately 80 to 100' thick in the
Illinois Basin. At its northernmost reaches where it grades in to the
Joliet and
Racine Formations it is about 150' thick.
Appearance
The St. Clair is composed of course calcite grains to fine grains. It may contain partings of claystone or
Mudstone. It can range in color from light-gray to chocolate brown, or even or purplish-black. Beds of pink
crinoid remains are also found with in this unit, mostly toward the base.
^Penrose Jr., R.A.F. (1891). "Manganese: its uses, ores, and deposits". Annual Report of the Geological Survey of Arkansas for 1890. 1: 101–102, 112–114, 124–128, 166–203, 214–215.
^Schrenk, Steven (September 2017). "The Grey American Limestone that Acts Like a Marble". The Slippery Rock Gazette: 36, 37.
^Willman, H. B.; Atherton, Elwood (1975). "Handbook of Illinois Stratigraphy: Illinois State Geological Survey". Handbook of Illinois Stratigraphy: Illinois State Geological Survey. Bulletin 95: 261.
^Amsden, Thomas W. (1968). "Articulate Brachiopods of the St. Clair Limestone (Silurian), Arkansas, and the Clarita Formation (Silurian), Oklahoma". Memoir (The Paleontological Society). 1: i–117.
JSTOR1315506.
^Craig, William (1968). The stratigraphy and conodont paleontology of Ordovician and Silurian strata, Batesville district, Independence and Izard counties, Arkansas (PhD). The University of Texas.