[meteorite-list] Moldavite Update

[MexicoDoug 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:).