[meteorite-list] Moldavite Update

From: MexicoDoug_at_aol.com <MexicoDoug_at_meteoritecentral.com>
Date: Thu Jul 21 13:55:13 2005
Message-ID: <6b.499cf090.30113b7a_at_aol.com>

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:).
Received on Thu 21 Jul 2005 01:55:06 PM PDT