[meteorite-list] Re: TEKTITES!! ....METEORITES OR JUST GLASS Obsidian

From: thornysahuaro <thornysahuaro_at_meteoritecentral.com>
Date: Thu Apr 22 10:08:31 2004
Message-ID: <20020925151128.93270.qmail_at_web20510.mail.yahoo.com>

Elton, Thanks for the explanation. It amazes me how knowledgeable the
members of this list are and how willing you are to share that knowledge.
Now, one more question. If I'm out collecting Apache Tears and I should
pick up a Tektite, how would I know the difference? If I happened to put
that tektite into the tumbler with a batch of Apache Tears would there be
any obvious differences when polished?
Art Brasher

--- EL Jones <jonee_at_epix.net> wrote:
> Let me try to get this one right the first time.
>
> This doesn't address the Lunar meteorite vs Ejecta debate but is a
> discussion on how volcanic glass-specifically "Apache Tears" forms
> Apache Tears as common term for nodular obsidian.
>
> The bulk content of the rock obsidian is silica, silicon dioxide-- SiO 2

> which is a light colored, "felsic" mixture. Notice I did not say
> "mineral". It is the relatively-fast cooling which forms glass, without
> allowing a crystalline structure to form nor, for other mineral-forming
> compounds to segregate to form a mineral--a subtle but technical point.
> The trace material's found in obsidian are from the "felsic to
> intermediate" BRS "pre- mineral compounds/ molecules". Bulk obsidian
> composition will be from the bottom (felsic) end of the BRS. and one
> would think it would be light in color. Obsidian is dark because, while
> it is a glass, it has many impurities which absorb light and make it
> appear dark.
>
> Apache tears are frequently found in stream beds were they have eroded
> from a softer "felsic" pumice/scoria-ash in which they form. So they may
> on first observation look as it they were spewed from a volcano high
> into the air. They are not ejected in the form they are found. They
> form after hot ash accumulates.
> droplets of silica glass accrete into developing gas pockets. This
> allows most gas to escape from within the glass as it pools and grows
> in non-crystaline fashion. Obsidian has a relatively high water content,
> interestingly enough . The "tear" is more dense than the scoria/pumice/
> tuft which is still highly gaseous. So it settles by this short-lived
> sorting action in bands within the ash.
> Apache Tears, therefore are a post-ejection form of obsidian which
> form rapidly and cease growing into larger veins of obsidian because the
> temperature of the scoria/ pumice ash falls below the threshold of the
> mineral formation in the lower end of Bowen's reaction series
>
>

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Received on Wed 25 Sep 2002 11:11:28 AM PDT