[Rockhounds] Obsidian in Michigan

[Paul van den Bergen]

Dacite is a type of lava slightly lower in silica than Rhyolite.  Obsidian
is common in Rhyolites.

Worth noting that all lavas have a large fraction of glass when erupted.
Rhyolites being high in Silica are both way more viscous and (presumably?)
have a lower crystalline fraction... though that may be entirely wrong.

On Tue, 20 Sept 2022 at 14:04, Tim Fisher <nospam at orerockon.com> wrote:

> Whoops forgot to say that if the location is Wagontire then it's
> technically
> dacite, not obsidian. There's a distinction but I don't know what it is. It
> definitely knaps easier.
>
> Tim Fisher
> Http://OreRockOn.com
> Email nospam at orerockon.com
>
> -----Original Message-----
> From: Rockhounds [mailto:rockhounds-bounces at rockhounds.drizzle.com] On
> Behalf Of Kreigh Tomaszewski
> Sent: Monday, September 19, 2022 5:50 PM
> To: Rockhounds at drizzle.com: A mailing list for rock and gem collectors
> Subject: Re: [Rockhounds] Obsidian in Michigan
>
> Obsidian has been found in Michigan, brought in by Native American's ~9,000
> years ago from Oregon.
>
> https://www.bendbulletin.com/localstate/researchers-trace-ancient-obsidian-i
>
> n-lake-huron-to-central-oregon/article_0481666a-d52d-11eb-b987-ebe7a8e28b33.
> html
> <https://www.bendbulletin.com/localstate/researchers-trace-ancient-obsidian-in-lake-huron-to-central-oregon/article_0481666a-d52d-11eb-b987-ebe7a8e28b33.html>
>
> I live in Lower Michigan, and if you go out in my yard you can find
> obsidian.
>
> Obsidian can be found in lower Michigan, but it was imported from somewhere
> else (or possibly dropped here by a glacier).
>
>
> 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
> >
> >
> >
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-- 
Dr Paul van den Bergen