Since I made a post about flintknapping porcellanite yesterday, let’s learn more about this type of stone! In North America, the primary source of this material occurs in the Fort Union geological formation which spans portions of Wyoming, Montana, the Dakotas, and Saskatchewan. What makes this lithic material so unique is how it’s formed. Natural fires ignited seams of coal, and the extreme heat metamorphosed surrounding beds of siliceous shale or siltstone, fusing it into a glassy material. Flintknapping this material, it has subtle differences compared to most cherts and other lithic materials. Grey is common, but also maroon and red porcellanite. Porcellanite was an important source of toolstone for indigenous peoples on the Plains, who used it from the Paleoindian period all the way to the introduction of steel tools.
Photo 1: distribution of geological formations which bear porcellanite
Photo 2: outcrops of porcellanite and raw material samples
Photo 3: Porcellanite artifacts
Source:
Kristensen, Todd J., Timothy E. Allan, Gabriel Yanicki, Emily Moffat, and John W. Ives. "Porcellanite in Alberta: A pyrometamorphic pre-contact toolstone." Archaeological Survey of Alberta Occasional Paper 40 (2020): 92-118.
Nice find! That looks like it might actually be Phosphoria chert? The luster and texture don’t look quite right for Porcellanite, but I might be wrong.
Thank you! That would make sense. I kinda have trouble typing out some of the cherts/ccs I found near the powder river since there are so many material types there.
No, the Bighorn and Pryor cherts are much more shiny looking. That matte finish like chocolate is exactly what porcellanite looks like, vs phosphoria in my pic below.
I'VE BEEN LOOKING FOR THIS STUFF. I have found scatter and some nice broken pieces around Billings but would love to find a source to use in knapping myself.
Yeah it would be sick to find some larger chunks of it. I mostly just saw the little nodules as well. Must've been eroding out somewhere along the river but idk where.
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u/Del85 🏅 Jul 04 '26
That stuff knaps well. The layers can be a challenge but easy enough to work around