[Jewelry making - Article 00094] - RE: [Orchid] ammonite

[Richard O. Martin]

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I haven't followed this string carefully and maybe someone else has 
mentioned this, but the gem ammolite now on the market is not opalised.  
In certain deposits, mainly in Canada, fossilized ammonite shell has 
been replaced by flat platelets of aragonite (calcium carbonate), 
according to scanning electron microscope studies by Henry L. Barwood, 
Ph.D.  The arrangement of these platelets causes "interference fire" 
instead of diffraction colors as with precious opal, he says.  When cut 
properly (some treatment is required, I understand), ammolite exhibits a 
brilliant play of color somewhat like opal.  The difference, according 
to Barwood, and I quote him, is that ammolite "tends to run to 'second 
order' reds and greens; opal typically exhibits 'primary' or first-order 
spectral colors of greater purity and intensity." 

Just thought you'd like to know in case you're on "Jeopardy" when the 
question comes up.

Rick Martin


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