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GeneralMissouri Chalcopyrite Iridescence?

3rd Oct 2019 19:26 UTCSteve Hardinger Expert

Are the iridescent Missouri chalcopyrite colors natural, or chemically-induced?

3rd Oct 2019 19:44 UTCtodd Van Duren

I've always taken them to be natural.  Certainly they've been around a long time, so if they are fake they've been faked for a long time, and I've never heard any view that was the case.

Iridescence is so common on chalcopyrite, why would you suspect they are fake? 

3rd Oct 2019 19:59 UTCKevin Conroy Expert

Some are natural, but the vast majority of the brightly colored iridescent ones (as in the included photo) are definitely chemically-induced.   I'm referencing the ones from the Viburnum Trend.   So far I've only seen the "fakes" from the mines in the Trend (and I hope I never see any from the other Missouri chalcopyrite localities).

3rd Oct 2019 20:36 UTCHarold (Hal) Prior Expert

I concur 100 percent with Kevin - I've viewed many 100 Missouri Chalcopyrites in the past 50 plus years and never saw one as bright as the picture that was confirmed as natural. Many years ago I saw a flat of Black Rock, Arkansas dolomite with a similar fantastic blue color for sale.  The seller assured me it was natural and told who had collected it.  The collector (a chemist) later told me he had dyed it and sold it at a flea market as dyed. 

3rd Oct 2019 20:41 UTCBob Harman

KEVIN is essentially correct. Those examples from the Viburnum trend with nice calcites on the specimen, in addition to the chalcopyrites, probably will be natural. 
If you look thru dealer stocks who have these, you can occasionally see specimens with both minerals. I have one such specimen.
This might be one way to acquire the natural examples      CHEERS.....BOB

3rd Oct 2019 22:05 UTCIan Nicastro

02872060015701366712958.png
There are absolutely chemical methods for bringing out the iridescence. I gifted a specimen of golden colored chalcopyrite on dolomite to a local mineral dealer friend who does specimen prep work and has access to all sorts of acids and chemicals, and he showed me the same piece weeks later and the chalcopyrite had turned all blue and purple. He did not disclose the chemical that was used.

3rd Oct 2019 22:29 UTCKevin Conroy Expert

Iron Out will do the "trick".

3rd Oct 2019 23:37 UTCtodd Van Duren

Iron Out will do the "trick".

As well as explain the very dull dolomite.  I must say, when I commented above, I can honestly say I've never seen a MO chalcopyrite THAT electric peacock blue, though I've certainly seen plenty of much more moderately iridescent examples. 

3rd Oct 2019 23:04 UTCChester S. Lemanski, Jr. Manager

Collected at an active Arizona mine - freshly blasted ore with chalcopyrite had the natural brassy color. Collected the same spot the next year - all the chalcopyrite had tarnished with the iridescent colors. Quite natural in that case.

3rd Oct 2019 23:50 UTCBen Grguric Expert

I've never tried it, but I've been told household bleach can be used.

4th Oct 2019 00:08 UTCGareth Evans

The crystal healing stores buy massive chalcopyrite that has been treated with acid to turn them an iridescent blue. Sometimes they sell them as Bornite because it apparently has better chakras than Chalcopyrite.  I have been told by the mineralogy chaps that bornite does sport an iridescence that is natural on exposure to air. I have chalcopyrites in my collection from different locals and none have turned blue - so I must be lucky. I suspect that if the chalcopyrite was also associated with pyrite that decomposed (as in ore bodies on exposure to moisture) then the decomposition products of pyrite could adversely affect the chalcopyrite. 

4th Oct 2019 05:38 UTCKeith Compton Manager

See also this Mindat post:

4th Oct 2019 07:00 UTCCecil Cosse

I have a large -- about 7 x 7 inch -- chalcopyrite from the Tri-State area bought in the like 1971 or 1972 that still has its somewhat brassy color.  I have never wanted it to have that bluish tarnish  It would look ridiculous.

Cecil

4th Oct 2019 11:57 UTCAntoine Barthélemy

I remember thinking that the bright blue one were suspicious when I first saw them. But since no one was questioning their authenticity, I considered them to be natural...

Glad you have raised the question, I have learned something new here!
 
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