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Techniques for CollectorsIridescent Andradite and an Ultrasonic Cleaner
29th Jun 2012 04:14 UTCNelse Miller
29th Jun 2012 04:21 UTCAlfredo Petrov Manager
29th Jun 2012 05:54 UTCStephanie Martin
Be careful mounting them. If they are tiny clusters then that "mud" may be holding them together. I have ruined a few while arranging them in tack, being too firm while trying to adjust the orientation to get the best colour play, the clusters can crumble. Single crystals are more robust.
regards,
stephanie :-)
29th Jun 2012 09:36 UTCRock Currier Expert
29th Jun 2012 12:00 UTCBart Cannon
The source of the iridescence is thought to be from polysyntheic twinning.
There is no way to remove that iridescence.
My old friend, the late Julian D. Barksdale wrote a paper about the deposit in the American Mineralogist.
I think it inspired the first color plate ever published in the AM.
He gave me his box of the material before he died.
They are just crumbs, but they have spectacular play of colors.
I still have a signed reprint of the article, but it is somewhere in the late paleocene strata of my stack of papers.
Googling Barksdale and polysynthetic twinned andradite, and American Minera might turn it up.
Bart
29th Jun 2012 13:04 UTCDavid Von Bargen Manager
29th Jun 2012 13:59 UTCNelse Miller
29th Jun 2012 14:10 UTCStephanie Martin
http://wwwsoc.nii.ac.jp/jepsjmo/cd-rom/2005cd-rom/pdf/k038/k038p-007_e.pdf
http://www.gemlab.net/gemlab/fileadmin/user_upload/Publications/RainbowAndradite-GG.pdf
this page has a diagram that explains the effect:
http://www.mineralienguild.com/rainbow/
hope this helps.
regards,
stephanie :-)
4th Oct 2012 16:29 UTCBart Cannon
I suggested that the colorful Nevada andradites were "iridescent".
Not quite true.
What they display is a subsurface "play of colors" probably derived from a form of twinning and the resulting interference colors.
J.D. Barksdale who authored an article in the AM speculated the color was due to an effect that he coined a name for..
Can't remember if that term was polychromatic twinning or polysynthetic twinning.
I have a box of crumbs showing the effect in the Nevada andradites. Free crumb to anyone with the gear to study them.
Bart
4th Oct 2012 17:29 UTCDmitry Stepanenko
I would like to make a comment as a specialist on ultrasonic technologies. Ultrasonic cleaning of surface contaminants is based on their delamination from the surface by oscillating gas bubbles dissolved in water (or other cleaning liquid). Bubbles penetrate under contaminant film and delaminate it. So, it is possible that cavitation (formation of oscillating and collapsing gas bubbles) delaminated layers (surface films or even thin layers of the crystal) involved in iridescence.
Best regards,
Dmitry.
P.S.: Dear Bart, is it possible to get a couple of Nevada andradites from you for collection and possible study? I'm very interested in iridiscence of garnets (see my recent post on iridescent garnet from China). We can discuss details via private messages. Thanks!
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