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Named stone

Madison Formation chert (Montana chert)

Also called Montana chert, Madison chert, Madison Limestone chert

A kind of chert (and flint)

Madison Formation chert (Montana chert)Chert (and flint)Rockies & Great Basin

Description

Archaeologists working on the northwestern Plains often lump the colourful cherts and chalcedonies from nodules in the Madison Limestone of southwestern Montana as "Montana chert". The colours run from purple to red, orange and yellow, often with branching black manganese dendrites and sometimes brachiopod fossils, and pieces can be mottled or variegated. Nodules reach cobble size, and the stone fractures very well, so it was valued toolstone. A few quarries give recognisable varieties: Everson quarry, pit-mined at the head of the Beaverhead River in the Madison formation, has clear to black chalcedony and yellow to red-brown chert, and Helena and Avon chert are named for quarries near those towns. A golden dendritic chert at the Besant-age Muhlbach site in Alberta is linked to Madison sources.

How to identify it

Colour
Purple to red, orange or yellow; sometimes variegated or mottled (Miller 1991, via Krahulic). Everson chalcedony: clear, white, tan-brown, chocolate brown or black; Everson chert: yellow to red-brown (Bonnichsen et al. 1992, via Krahulic). A golden dendritic chert is linked to Madison sources (Roll et al. 2005, via Graham).
Texture
Excellent fracture; high-quality toolstone (de Mille 1997, via Krahulic). Everson stone is homogeneous, transparent to opaque (Krahulic).
Luster
Everson chert and chalcedony: vitreous (Krahulic).
Inclusions
Manganese oxide dendrites and in some pieces brachiopod fossils (Miller 1991, via Krahulic).

Geology

Nodules of chert and chalcedony, up to cobble size, in the Madison Limestone of southwestern Montana (Miller 1991, via Krahulic).

Where it comes from

Rockies & Great Basin, Plains

States

Quarries and outcrops

  • Madison Limestone outcrops, southwestern Montana (Krahulic)
  • Everson quarry, head of the Beaverhead River drainage, 2,197 m elevation; hundreds of quarry pits (Bonnichsen et al. 1992, via Krahulic)
  • Helena and Avon chert quarries, Montana (Krahulic; the thesis does not say these are in the Madison)

Used by

  • Old Women's phase sites, southern Alberta: Montana cherts identified in lithic assemblages (Krahulic 2016)
  • Besant, Muhlbach site, Alberta: points and flakes of a golden dendritic chert typically linked to Madison Formation sources (Graham 2014)

Look-alikes

Stones that are easy to confuse with Madison Formation chert (Montana chert).

  • Helena chert: opaque, creamy yellow to dark brown with dendrites; the "broken crayon" texture is the quarry-specific variety (Krahulic)
  • Avon chert: beige to white with a white or light grey patina, dull, often with gastropod fossils (Krahulic)
  • Banff chert (Alberta and northern Montana): black to dark grey-blue with thin light bands (Krahulic)

Sources

  1. Krahulic, Tobi L. 2016. Determining the Mobility of Old Women's Phase People on the Southern Alberta Plains as Evidenced by Lithic Assemblages. MA thesis, Department of Archaeology, University of Calgary.ucalgary.scholaris.ca (opens in a new tab)
  2. Graham, Reid Jordan. 2014. Breathing New Life into Old Records: Analysis of the Muhlbach and Stelzer Sites on the Northern Plains. M.A. thesis, University of Alberta.ualberta.scholaris.ca (opens in a new tab)

All materials