[Rockhounds] Obsidian in Michigan (Paul van den Bergen)

[Tim Fisher]

Yes that has been posted to Facebook (mea culpa). If people only glance at the headline it's their own damn fault lol. It doesn't surprise me at all, Oregon obsidian has been found in the southeast as well. The date of 9000 years old for the site does surprise me. I hope they have really good backup for that date (I confess to not having read the paper). My WAG is that would be the farthest known trade in anything at that time. And they missed a slight nuance about the material, the Wagontire exposure is more on the dacite end of the obsidian spectrum (I know the site well and have collected it there a couple times). The paper compares it to the flow on North Sister in the central Cascades, which is also dacite. It knaps better than most obsidian (e.g. Glass Buttes, OR which is less than 50 miles west, or Davis Creek, CA). One customer told me it knaps "like butter", but I don't think butter knaps very well). So it would have been worth comparatively more than obsidian from most other western state sites.

Tim Fisher
Http://OreRockOn.com 
Email nospam at orerockon.com

-----Original Message-----
From: Rockhounds [mailto:rockhounds-bounces at rockhounds.drizzle.com] On Behalf Of Paul
Sent: Wednesday, September 21, 2022 9:22 AM
To: Rockhound List
Subject: [Rockhounds] Obsidian in Michigan (Paul van den Bergen)

On Mon, Sep 19, 2022 at 7:05 PM <gbrown at catspaw-minerals.com> wrote:

 > Hi Kids...
 >
 > I'm in a Facebook argument about obsidian in lower Michigan.
 > They don't believe me when I say NOPE.
 > *sigh*
 > Gary

I agree with Gary. The volcanic rocks of the Canadian Shield are much too old to contain and be a source of obsidian. Any obsidian that these rocks once contained have long since been either recrystallize to chert, altered to clay minerals and zeolites, and / or recrystallized by metamorphism.

The occurrence of obsidian in Michigan is discussed in the below open access paper:

O’Shea, J.M., Lemke, A.K., Nash, B.S., Sonnenburg, E.P., Ferguson, J.R., Nyers, A.J. and Riebe, D.J., 2021. Central Oregon obsidian from a submerged early Holocene archaeological site beneath Lake Huron.
PloS one, 16(5), no.e0250840.

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0250840
https://www.researchgate.net/publication/351720833_Central_Oregon_obsidian_from_a_submerged_early_Holocene_archaeological_site_beneath_Lake_Huron

Yours,

Paul H.


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