[meteorite-list] Moldavite Update

From: Norm Lehrman <nlehrman_at_meteoritecentral.com>
Date: Thu Jul 21 14:35:49 2005
Message-ID: <20050721183534.23231.qmail_at_web81003.mail.yahoo.com>

All,

I have access to a PIMA (portable infrared mineral
analyzer). These operate on spectral reflectance in
the SWIR spectrum (1300-2500 nanometers). There are
excellent water absorption features in this range.
I'm sure I've run tektites before, but never in direct
comparison with volcanic and man-made glasses. I'll
do this next time I'm back in the office and report
back. I do still have one of the chinese bottle-glass
pseudotektites somewhere if I can find it--

Regards,
Norm
http://TektiteSource.com

--- mafer_at_imagineopals.com wrote:

> Greetings Doug and List
>
> There may be a non-destructive test that isn't as
> costly as a microprobe
> for tektites.
>
> XRF was used by the Geology & Archaeology
> departments at WWU to check a
> flake (known artifact) against normally prepard XRF
> samples for composition
> similarities (for tracing the source outcropping of
> the material that flake
> was made of). This proved to be a viable alternative
> to destructive testing
> of artifacts, as long as exact results were not
> required and a relatively
> flat surface could be presented to the XRF and the
> sample would fit into
> the recepticle. It was thought that XRD would also
> work as well, given the
> same restrictions.
>
> Many universities would have these devices, as
> opposed to those that have
> microprobes. And it would be a matter of setting up
> a database with known
> trace elements/minerals and look for the same in the
> XRD or XRF results.
>
>
> Just a thought.
>
> Mark Ferguson
>
>
>
>
>
> On July 21, 8:55 pm MexicoDoug_at_aol.com wrote:
> > John G. wrote:
> > > Since moldavites are made basically of the same
> material as green
> > > pop bottles, checking the refractive index of a
> faceted stone
> > > wouldn't turn up anything suspicious...looking
> for new technology
> > > to tell the difference between the fakes and
> the real stones.
> >
> > Hola John, List,
> > Not as easy as looking at a Shirokovsky
> 'pallasite', either, where
> > just one fake is well known. This seems a lot
> scarier than getting a
> > "synthetic" diamond in place of a "real" one since
> an appreciation of
> > history is what makes the glass authentic for the
> owner, like a
> > winning game ball, and for the sake of science a
> confidence in it
> > being of tektite origin necessary for future
> ability to study
> > composition of a real sample is at stake.
> > In the case of tektites, unless you have the
> ability to make
> > non-destructive measurements with expensive
> microprobes, I guess the
> > technique of choice will need to hinge on the
> difference tektites
> > have over man-made glasses: low water content.
> >
> > Water has major IR absorbance peaks at 3550, 3425,
> 3295, 1630 and
> > 1455 /cm. An appropriately set IR analyzer at one
> or more of these
> > frequencies ought to be able to able to make a
> positive
> > identification vs. other glasses (and confirming
> your refractive
> > index wouldn't hurt at all). While I've never
> done these types of
> > IR measurements in glasses, it would seem that
> all you just need to
> > watch out for would be humidity, and to know your
> sample path length
> > reasonably. Other tests would rely more on
> variable criteria
> > depending on recognizing characteristics of the
> fake, sometimes easy,
> > but sometime not. Tektites should yield about
> 0.001% to 0.03% water,
> > with moldavites a very typical 0.01% (100 ppm).
> I don't know what %
> > water recast glass from coke bottles, etc., but I
> am guessing it
> > would be much higher unless great pressures and
> long times in the
> > casting furnace were used. Anyone know the
> solubility of water in
> > glass at melt conditions? I'm guessing - 10 -
> 100 times that
> > amount? Saludos, Doug (where the neighborhood
> streets are still a
> > grid of rivers, in the aftermath of the fight
> between Emily and our
> > mountains. Emily lost decisively as her Eye
> passed 80 km south.)
> > It is refreshing to see water under the USD
> 50,000,000 bridge we
> > just built over the otherwise dry riverbed. The
> collosal "bridge"
> > is a copy of the one in Rotterdam for our inland
> city nicknamed
> > "City of Mountains" nestled in the Sierra
> Madre:).
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Received on Thu 21 Jul 2005 02:35:34 PM PDT