Named stone
Jefferson City-Cotter chert and Mozarkite
Also called Jefferson City chert, Cotter chert, Mozarkite (Missouri state rock)
A kind of chert (and flint)
Jefferson City-Cotter chert and MozarkiteChert (and flint)OzarksDescription
Jefferson City and Cotter chert comes from the Early Ordovician Jefferson City and Cotter dolomites of the Ozarks, which archaeologists often treat as one Jefferson City-Cotter unit. It and Burlington chert dominate many Ozarks stone tool collections, and both were heat treated; an experiment found heating improves the flaking of each. Mozarkite, Missouri's state rock since 1967, is the colourful mottled and pink variety: chert with chalcedony in reds, pinks and purples tinted green, gray and brown, which takes a high polish. Missouri's survey places Mozarkite in the Cotter Dolomite, about 450 million years old, as residual boulders on hillslopes and roadcuts, mostly in west-central Missouri south of the Missouri River and west of the Lake of the Ozarks, centred on Benton County. Cotter chert nodules often show concentric light and dark bands.
How to identify it
- Colour
- Mozarkite: red, pink and purple with tints of green, gray and brown (Missouri Geological Survey). Cotter chert nodules often have concentric light and dark bands (Arkansas Geological Survey).
- Luster
- Mozarkite takes a high polish.
- Inclusions
- Mozarkite contains varying amounts of chalcedony.
- Heat treatment
- Ozarks assemblages show ample heat treatment of Jefferson City chert, and experiments found heating improves its flaking (Byers, Picka and Ray 2014; Picka 2012). The colour change on heating was not described in what was opened.
Geology
Early Ordovician Jefferson City Dolomite (light to dark tan dolostone with considerable chert) and Cotter Dolomite of the Ozark Plateaus in Missouri, northern Arkansas and Oklahoma. Missouri's survey places Mozarkite in the Cotter Dolomite, about 450 million years old, weathering out as residual boulders in soil.
Where it comes from
Ozarks
Quarries and outcrops
- Benton County, Missouri, and nearby (Mozarkite; collecting began there in the early 1950s)
- West-central Missouri south of the Missouri River and west of the Lake of the Ozarks
- Jefferson City and Cotter dolomite outcrops across the Missouri and Arkansas Ozarks
Used by
- Heat-treated Jefferson City chert at the Big Eddy site, southwest Missouri (Byers, Picka and Ray 2014); the periods involved were not stated in the abstract
Look-alikes
Stones that are easy to confuse with Jefferson City-Cotter chert and Mozarkite.
- Burlington chert, the other dominant Ozarks chert, also heat treated
Sources
- Missouri Department of Natural Resources, Missouri Geological Survey. 2015. Mozarkite: Missouri's Official State Rock. PUB0653.dnr.mo.gov (opens in a new tab)
- Missouri Secretary of State. Missouri State Rock and Lithologic Emblem (Mozarkite).sos.mo.gov (opens in a new tab)
- Missouri Department of Natural Resources, Missouri Geological Survey. 2016. Chert. PUB0661.dnr.mo.gov (opens in a new tab)
- Arkansas Geological Survey. Ordovician Period of the Ozark Plateaus in Arkansas.geology.arkansas.gov (opens in a new tab)
- Byers, David A., Craig Picka and Jack H. Ray. 2014. Heat Treatment, Ozarks Cherts, and Prehistoric Toolstone Use in Southwest Missouri. American Antiquity 79(3):507-521.cambridge.org (opens in a new tab)
- Picka, Craig Matthew. 2012. Heat Treatment of Ozark Cherts: An Archaeological Experiment in the Effects of Heat Treatment on Toolstone Flaking Properties. M.S. thesis, Missouri State University.bearworks.missouristate.edu (opens in a new tab)
- Ray, Jack H. 2013. Stateline Faults: Making a Case for Standardized Terminology in Lithic Studies from an Ozarks-Wide Perspective. The Arkansas Archeologist 51:25-41 (supplemental colour figures).arkarch.org (opens in a new tab)