[meteorite-list] Moldavite Update

[mafer at imagineopals.com]

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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