[meteorite-list] Tektite identification criterion

From: N Lehrman <nlehrman_at_meteoritecentral.com>
Date: Thu Apr 22 09:53:35 2004
Message-ID: <003601c2a7e4$c567ee20$19e3fea9_at_homeportal.2wire.net>

Jim and all,

Thanks for breaking solitude to reply. Your suggestion is a great one.
It's remarkable how many highly esoteric features can be indirectly assessed
by reasonably simple techniques. The torch test addresses the exceedingly
low volatile content of virtually all tektite glass which contrasts sharply
with virtually all terrestrial glass. For those of you that have been
following this discussion, Jim's test is certainly more universal and
diagnostic than the magnetic susceptibility test I described. Combine the
two, and you should have an answer that you can take to the bank.

If it were essential to take yet another step---as in the case where it
looks like you've got a candidate for a "new" tektite---- my next suggestion
would be thin-section petrography looking specifically for lechatelierite
(+) and microphenocrysts(-). While not a field test, this is still a
reasonably inexpensive step that is readily commercially available. There
are a few other glasses out there with lechatelierite, but if you've got a
low-volatile glass, devoid of crystallites, with reduced iron, and
containing lechatelierite "worms", I think the argument is all over. Do you
concerned folks agree?? Do you have additions, revisions, comments, or
corrections? I'd love to get the subject of tektite verification reduced to
a reasonably solid, simple formula.

P.S., Jim, please do send me the images you described. Thanks again.

Norm
TektiteSource.com


----- Original Message -----
From: "James Tobin" <jimmypaul_at_earthlink.net>
To: "N Lehrman" <nlehrman_at_nvbell.net>
Sent: Thursday, December 19, 2002 7:19 PM
Subject: Re: [meteorite-list] Tektite identification criterion


>
> Hi list,
> I seldom post, but could not resist this topic. The simplest test for
> identification of tektites from any volcanic glasses no matter how
> tektite-like they look; is to put a sliver in an oxy-acetylene flame and
> see what happens. Volcanic glasses will froth into pumice instantly and
> true tektite glass will do nothing but blind you from the incandescence.
We
> have posted pictures of this before. Anyone interested can ask off list
and
> I will send them pictures of samples that have been through this test.
>
> The funniest part of this is even after you do the visual examinations and
> other tests, when there is no doubt that the sample is ordinary obsidian
or
> something similar. Most of the senders will insist that they are going to
> have more tests done. Because they "know" they are tektites. Just the same
> way it goes with meteor-wrongs. They "know" it is a meteorite because
> grandpa found it.
>
> Paul and I are in the midst of an ongoing research program with Stephen
> Pierce the staff geologist at Meteorite Times. He's taking absorption
> spectra of many natural glasses and man-made glasses. We are preparing the
> samples for him as thin two side polished flats. The result are very
> interesting. If you have not read the first portion of the results you can
> find the report in the back issues of Meteorite Times.
>
> It may be months before I say anything again, so let me take this time to
> wish you all a healthy and safe holiday season and new year full of joy.
>
> Regards
> Jim Tobin
> jim_at_meteorite.com
> The Meteorite Exchange
>
>
> > [Original Message]
> > From: N Lehrman <nlehrman_at_nvbell.net>
> > To: <mafer_at_domafer.com>
> > Cc: <meteorite-list_at_meteoritecentral.com>
> > Date: 12/18/02 11:24:49 PM
> > Subject: Re: [meteorite-list] Tektite identification criterion
> >
> > Mark and list,
> >
> > Properties like those you've listed do show helpful variations, but the
> range between individual tektite types tends to overlap with terrestrial
> materials to the point that none of this allows one to discriminate
between
> tektites and other materials.
> >
> > Despite the thousands of papers debating the myriad mysteries of tektite
> lore, I don't know of any that directly address the fundamental question
> "how do you tell if something is or is not a tektite?". I'd love to hear
> from any of you out there with ideas or suggested references.
> >
> > I'm going to pull a synthesis of this subject together with time, and
> there is a reasonable stash of widely scattered data that bear on the
> subject. The really big challenge though is coming up with criteria that
> can be used outside of a major university laboratory setting. For
example,
> one of the hallmark characteristics of tektite glass is its exceedingly
low
> water content. However, you'd be hard pressed to find any commercial
> laboratory that could provide an accurate determination of this property
at
> the levels of resolution we require. Ditto a good ion microprobe
analysis.
> This is all great stuff in the academic laboratory settings where most
> technical publications originate, but what are we supposed to do out here
> on the front lines?
> >
> > Of course, there are great folks in academia who will collaborate on
> worthy issues, but such matters cannot extend to passing judgment on
> suspect materials that arrive in the mail every other week. You meteorite
> freaks know the routine well---and have developed a pretty good bag of
> tricks to screen the winners from the losers. With tektites, we've barely
> emerged from debating the very definition of the word.
> >
> > Cheers,
> >
> > Norm
> > (TektiteSource.com)
> > ----- Original Message -----
> > From: mafer_at_domafer.com
> > To: N Lehrman
> > Cc: meteorite-list_at_meteoritecentral.com
> > Sent: Wednesday, December 18, 2002 8:46 PM
> > Subject: Re: [meteorite-list] Tektite identification criterion
> >
> >
> > Hi Norm and list
> >
> > Norm, are there any other tests that may prove useful like refractive
> indice, specific gravity or thermal conductivity? I mention these because
> of tektites having mineral contents not normally associated with
> terrestrial rock or glass, and I don't know if tachylytes would be of
> concern or not.
> > Mark flexing new old knowledge without a lot of experience
> > ----- Original Message -----
> > From: N Lehrman
> > To: meteorite-list_at_meteoritecentral.com
> > Sent: Wednesday, December 18, 2002 8:46 PM
> > Subject: [meteorite-list] Tektite identification criterion
> >
> >
> > List,
> >
> > New subject! At the TektiteSource.com, we've been bombarded with a
> stream of tektite wannabes (Texas, Arizona, Tanzania----). I've been
> struggling to find a reasonably simple tektite test that doesn't require
an
> ion beam microprobe, etc. to do. I've thought about the following
approach
> for a while, but just never got around to trying it till today. The basic
> concept is that true tektites typically contain absolutely no primary
> crystallites (except for Muong nongs which occasionally do have remnant
> mineral grains from incompletely melted target material). Only
> crystalline materials can assume magnetic properties, so without crystals,
> no magnetic susceptibility. Further, tektite glass is highly reduced
> (i.e., low volatile Oxygen), so even if it were to have microcrystals,
they
> would not be magnetite. The black or green color of tektite glass is from
> elemental iron literally dissolved in the glass, in which form it has no
> magnetic properties.
> >
> > On the other hand, nearly all volcanic glasses contain crystallites
> or phenocrysts. Since iron is abundant in the earth's crust and magnetite
> crystallizes at relatively high temperatures, it is an early-forming
> mineral---that is, if there were any crystals starting to form, magnetite
> would likely be there. Magnetite is, in fact, common in obsidian,
> sometimes causing the black coloration.
> >
> > From this line of thought, a fairly simple test is obvious: check
for
> magnetic properties. To nail this down in more quantified terms, I used a
> digital magnetic susceptibility meter available to me through work (mag
> susc. basically relates to the volume content of magnetic minerals like
> magnetite, titanomagnetite, ilmenite, pyrrhotite and native iron). In
> effect, the magnetic properties of the specimen provide an indirect way of
> assessing the presence of crystallites AND the redox state of the
material,
> both of which are good solid criteria for tektites vs. terrestrial
> volcanics.
> >
> > I'll post details after they're a bit more refined, but the basic
> pattern matches the theory: true tektites have extremely low magnetic
> susceptibilities; obsidians, apache tears, and amerikanites all yield
> values 2 to 10 times higher, with no field of overlap. Impactites (which
> very commonly contain Ni-Fe inclusions, are commonly 1 to 2 orders of
> magnitude higher than the tektites.
> >
> > Most people don't have access to a magnetic susceptibility meter,
but
> these differences are sufficiently large to detect with a strong magnet.
I
> tried a suspended neodymium/samarium magnet and got no reaction on any of
> my actual tektites. I did get subtle deflections with the tektite
wannabes
> I was checking, and it goes without saying that some of the impactites
> jumped out and clung to the magnet.
> >
> > The sweet and simple conclusion to all this is that when faced with
a
> suspect tektite, test for subtle magnetic properties. They may not always
> be detected by the simple magnet test---but if the material deflects a
> strong magnet, it's not a tektite.
> >
> > This may seem like esoteric trivia to some of you, but what you've
> just read is to my knowledge the first suggested simple field test to
> discriminate between tektites, terrestrial volcanics, and impactites. Of
> course, there are exceptions to most every rule, but so far it's looking
to
> me like this will put you on the right side of the argument about 99% of
> the time.
> >
> > Merry Winter Solstice and a Happy New Orbit to All!
> >
> > Norm
> > (TektiteSource.com)
> >
>
>
>
>
>
Received on Fri 20 Dec 2002 12:00:51 AM PST