St Clair Limestone (geologic formation)
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 Silurian period. It is high density, high magnesium dolomitic limestone. 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. 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. The St Clair is designated as a member of the Bainbridge Group in the State of Indiana. 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.Physical characteristics
| Imperial | Metric | ||
| Absorption by weight | ASTM C97 | 0.5% | 0.5% |
| Density | ASTM C97 | 168 lb/ft3 | 2 691.10 kg/m3 |
| Compressive strength | ASTM C170 | 15 889Psi | 109.55MPa |
| Modulus of rupture | ASTM C99 | 972Psi | 6.70MPa |
Paleofauna
[Brachiopod]s
Source:AncillotoechiaAntirhynchonellaAtrypa Atrypina BoucotidesBrachymimulusCymostrophia DicamaropsisDicoelosiaDolrorthisEospiriferHirciniscaHomoeospirellaHowellellaKozlowskiellinaLeangellaLeptaena Lissostrophia MeristinaNanospiraNucleospiraOnychotretaOrthostrophellaOxopleciaParastrophinellaPlacotriplesiaPlectatrypaPlectodonta PlicocyrtiaResserella Shaleria Streptis- ''Virginiata''
[Conodont]s
Source:AcodusAmbalodusBelodellaBelodinaCarniodusCordylodusDistacodusDistomodusDrepanodusHadrognathusHindeodellaLigonodinaNeoprioniodusOistodusOzarkodinaPaltodusPanderodusPlectospathodusPterospathodusSpathognathodus- ''Trichonodella''