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

[Paul]

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.