Mount Carroll Quarry, Mount Carroll, Carroll Co., Illinois, USA
|Latitude & Longitude (WGS84):||42° 5' 3'' North , 90° 1' 47'' West|
|Latitude & Longitude (decimal):||42.08444,-90.03000|
|Köppen climate type:||Dfa : Hot-summer humid continental climate|
Dolostone quarry west of Mount Carroll, Illinois, located immediately north of Illinois Route 64/U.S. Route 52, 2 1/2 miles west of the intersection with Illinois Route 78.
The quarry exploits the Wise Lake and overlying Dubuque formation of the Ordovician-age Galena Group. The Wise Lake consists of hard, dense, light grey dolostone with scattered small mineralized vugs (mostly mm-size marcasite and pyrite on minute sparkling white rhombs of dolomite; sphalerite, galena, and barite are less common). The Dubuque consists of softer, darker, yellower dolostone with more, larger mineralized vugs (cm-size marcasite, pyrite, sphalerite, yellow barite, and galena; calcite, smithsonite, and cerussite? are rare) and occasional petroluem-filled cavities. The Ordovician-age Maquoketa Shale is present as overburden.
Marcasite from Mt. Carroll appears to be relatively stable, with no deterioration noted as yet (2015) in dozens of specimens collected by E. L. Clopton in the 1980s and 90s and subjected to seasonal extremes of humidity and dryness since then. Several specimens of Mt. Carroll pyrite, however, have deteriorated.
8 valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
252.17 - 541 Ma
|Paleozoic sedimentary rocks|
Age: Paleozoic (252.17 - 541 Ma)
Lithology: Sedimentary rocks
Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. 
|Katian - Sandbian|
445.2 - 458.4 Ma
|Galena Group (Trenton Limestone)|
Age: Late Ordovician (445.2 - 458.4 Ma)
Comments: Thickness from stratigraphic column for northern Illinois (north of 40 degrees north latitude), from oldest to youngest: Decorah Fm (0-25’), Dunleith Fm (0-135’), Wise Lake Fm (0-80’), and Dubuque Fm (0-40’). Unit is listed as the Galena - "Trenton" Group on the stratigraphic column for northern Illinois (north of 40 degrees north latitude). The Decorah Formation is comprised, from oldest to youngest, of the Spechts Ferry Shale, Millbrig K-bentonite Bed, and Guttenberg Dolomite according to the stratigraphic column on the back of the geologic map.
Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052.