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Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?
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bob kerr




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PostPosted: Jun 03, 2018 09:42    Post subject: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

I think everyone has seen the incredible “electric blue” azurites from the Milpillas Mine in Mexico. It is generally thought that the electric blue color results from a very thin final coating of azurite over a malachite-after-azurite pseudomorph. (Paragenisis: azurite morphs to malachite then is re-coated with a very thin layer of azurite.)

Many of these electric blue specimens seem to be “associated” with malachite – that is, there is an abrupt end to the thin, electric blue azurite coating then the malachite (usually fibrous) starts. (See examples in the first three photos below.)

So - does where the azurite end constitute a natural transition to the underlying malachite (i.e.; the final azurite growth stopped there) - or has the thin final azurite layer been chipped off – fully or partially - exposing the underlying malachite (i.e.: a damaged specimen)?

I think the correct answer is “yes”. That is, it can be natural, chipped and natural AND chipped - or somewhat re-healed??

I posed this question to a few of - what I would consider - knowledgeable higher end dealers selling such specimens and the answer was pretty much “it’s natural – the azurite coating just failed to fully cover the malachite”. Examining closer with a strong loop though – they were not so sure.

I’ve attached two additional photos (the fourth and fifth photos below - taken from a microscope - not the best quality) showing examples of the transition point between the azurite and malachite. These photos were both taken from the specimen shown in the third specimen photo. In one photo, I think it is clear that the transition is natural – azurite faces show right up to the malachite field. The next photo shows what I think is chipped azurite at the interface exposing the underlying malachite. The underlying fibrous malachite appears undamaged.

I guess the main point of this post is: know what you are buying - “caveat emptor”. Even major dealers are unclear here. (I do not think, however, that a significant amount of intentional misrepresentation is present. Maybe I’m being naïve.) I have purchased a number of these wonderful pieces thinking the transition was natural – and to the naked eye, they sure appear to be – and the exposed fibrous malachite field appears undamaged. But after closer examination, I think many (most?) are chipped. Even some that are mostly natural in the transition region have some chipping involved – the azurite is just so thin and delicate that specimen removal and transportation – or even basic specimen cleaning - could cause this
.
I’d like to hear what others think here also – especially Mexican experts like Pete Megaw.

bob



example 1.JPG
 Mineral: Electric Blue Azurite and Malachite - example 1
 Locality:
Milpillas Mine, Cuitaca, Municipio Santa Cruz, Sonora, Mexico
 Description:
Example 1
 Viewed:  8767 Time(s)

example 1.JPG



example 2.JPG
 Mineral: Azurite and Malachite - example 2
 Locality:
Milpillas Mine, Cuitaca, Municipio Santa Cruz, Sonora, Mexico
 Description:
Example 2
 Viewed:  8759 Time(s)

example 2.JPG



example 3.JPG
 Mineral: Azurite and Malachite - example 3
 Locality:
Milpillas Mine, Cuitaca, Municipio Santa Cruz, Sonora, Mexico
 Description:
Example 3
 Viewed:  8780 Time(s)

example 3.JPG



interface 1 of example 3.jpg
 Mineral: Azurite and Malachite - natural interface
 Locality:
Milpillas Mine, Cuitaca, Municipio Santa Cruz, Sonora, Mexico
 Description:
This is what I think is a natural interface between azurite and malachite
 Viewed:  8758 Time(s)

interface 1 of example 3.jpg



interface 2 of example 3.jpg
 Mineral: Azurite and Malachite - chipped(?) interface
 Locality:
Milpillas Mine, Cuitaca, Municipio Santa Cruz, Sonora, Mexico
 Description:
I think this is a "chipped" (maybe partially re-healed??) interface between azurite and malachite
 Viewed:  8752 Time(s)

interface 2 of example 3.jpg


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Bob Harman




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PostPosted: Jun 03, 2018 10:50    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

At the prices shown for those examples, the ONLY way to accurately access the crystal and specimen edges for chips, dings, color variations vs. natural notches and irregularities etc is up close and IN PERSON EXAMINATION!. In fact it almost always is a combination of all of the above, but to accurately access the EXTENT of chips and dings vs natural changes, in person examination seems mandatory.

Photos, even good quality ones, just don't do it regarding pricy specimen quality for me. I personally have never purchased an expensive specimen without personal inspection and I never will....... BOB
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PostPosted: Jun 03, 2018 12:11    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

To quote Frank Zappa...."yes, yes, I've always said yes"

These can go both ways. I check mine carefully with a 20X handlens and a scope. I've seen it go both ways...damage and fully crystallized...even in the same piece. Given how many specimens from Milpillas are damaged/tipped it should be routine to check all terminations carefully.

I love these when the tips are natural with the green poking through.
The central crystal here shows the sharp terminations on the azurite around the malachite.



20171209_081827.jpg
 Mineral: Azurite on malachite ps azurite
 Dimensions: 18 x 14 x 3 cm
 Description:
Largest crystal is 12 cm. Malachite tips are natural...surrounded by well crystallized azurite.
 Viewed:  8754 Time(s)

20171209_081827.jpg



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Bob Morgan




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PostPosted: Jun 03, 2018 15:02    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

At the last Rochester Mineralogical Symposium J. Straw and John Betts presented a talk on azurite psudomorphosing to malachite from the inside out. Perhaps this is what these specimens show.
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PostPosted: Jun 03, 2018 19:40    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

Peter Megaw wrote:
To quote Frank Zappa...."yes, yes, I've always said yes"

These can go both ways. I check mine carefully with a 20X handlens and a scope. I've seen it go both ways...damage and fully crystallized...even in the same piece. Given how many specimens from Milpillas are damaged/tipped it should be routine to check all terminations carefully.

I love these when the tips are natural with the green poking through.
The central crystal here shows the sharp terminations on the azurite around the malachite.


thanks Pete - and WOW! I would've rejected that specimen as damaged without even getting out the loop - mainly because it looks like the green tipped azurite points appear incomplete - that is, the tips are shorter than seems natural.

so I guess it can go both ways - you could buy one that appears natural and is chipped - or reject one that appears chipped but is natural.

in any event - I wish I could've read about this important detail sooner - I'm not a fan of leaning by fire - I'd rather lean from someone else's experience.

thanks again,
bob
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PostPosted: Jun 03, 2018 19:41    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

Bob Morgan wrote:
azurite psudomorphosing to malachite from the inside out..


bob - maybe you could clarify this? never heard this term before.

thanks,
bob
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PostPosted: Jun 03, 2018 20:27    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

Good call on the term, What they were reporting is the development of malachite pseudomorphs after azurite. The change from azurite to malachite was from the inside outward, leaving the remaining azurite as the outer surface when the alteration wasn't complete.
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PostPosted: Jun 03, 2018 20:41    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

Bob Morgan wrote:
Good call on the term, What they were reporting is the development of malachite pseudomorphs after azurite. The change from azurite to malachite was from the inside outward, leaving the remaining azurite as the outer surface when the alteration wasn't complete.



ok - gotcha. I don't think this is what's going on here but will bow to more knowledgeable people. I think for these Milpillas pieces, the thin layer of azurite was deposited on top of the malachite after azurite pseudomorph.

thanks,
bob
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PostPosted: Jun 03, 2018 22:31    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

bob kerr wrote:
Bob Morgan wrote:
Good call on the term, What they were reporting is the development of malachite pseudomorphs after azurite. The change from azurite to malachite was from the inside outward, leaving the remaining azurite as the outer surface when the alteration wasn't complete.



ok - gotcha. I don't think this is what's going on here but will bow to more knowledgeable people. I think for these Milpillas pieces, the thin layer of azurite was deposited on top of the malachite after azurite pseudomorph.

thanks,
bob


Bob,

I remember that Bob Jones explained in detail about how these specimens with the electric blue color formed on an episode of What's Hot in Tucson several years ago.

Don

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PostPosted: Jun 04, 2018 08:47    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

Bob Morgan wrote:
At the last Rochester Mineralogical Symposium J. Straw and John Betts presented a talk on azurite psudomorphosing to malachite from the inside out. Perhaps this is what these specimens show.

Bob,

is this talk reported or recorded anywhere? I ask because this phenomenon isn't confined to Milpillas...it is also seen in specimens from the finds at Sepon in Laos in the past few years. (I'll try and attach a picture here), and I have puzzled over how it comes about, as both the "inside-out replacement" and "later overgrowth" ideas seem to me to have problems.

1. Inside-out replacement (it isn't pseudomorphing, as the replacement does not retain the form of the original, so what we see is a diagenetic recrystallization) is difficult to explain in a couple of ways. Firstly, it would be necessary for there to have been two phases original of azurite growth, the early one susceptible to the diagenetic change to malachite, the second one not susceptible. The second, final, phase would have to have the same thickness in all cases...and oddly, it appears to be the same at both Milpillas and Sepon. Secondly, if I am correct in assuming that the recrystallization is a result of fluid infiltration and not simply temperature and pressure changes, the fluids responsible would have had to had access to the cores of all of the crystals through final growth of azurite. That does not seem plausible.

2. A second growth of azurite over an earlier replacement malachite (or maybe fibrous primary malachite at Sepon) is also potentially problematic as the fibrous malachite substrate is unlikely to be a surface conducive to the growth of large crystal faces: the many potential nucleation points would result in the growth of many small crystals that could/would ultimately amalgamate. This is nicely illustrated in the first of Bob K's photomicrographs. This is congruent with the appearance of many of the crystals Bob's azurite specimens, but the one that Peter illustrates is dominated by large, planar faces, which would seem at odds with the amalgamation of many smaller crystal nuclei.

Overall, applying the joint scientific principles of Occams Razor and The Theory of Least Resistance, I have concluded that the answer is overall more likely to be the second idea, rather than the first, but would still be interested to learn of the conclusion of Messrs Straw and Betts supporting idea One.



Sepon Azurite.jpg
 Mineral: Azurite with Malachite
 Locality:
Khanong open pit, Sepon Mine, Vilabouly District, Savannakhét Province, Laos (Lao P.D.R.)
 Dimensions: 14 x 10 x 5 cm
 Description:
 Viewed:  8379 Time(s)

Sepon Azurite.jpg



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PostPosted: Jun 04, 2018 09:30    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

Hi, Bob.Kevin, list

I adhere to what Kevin said..
Azurite is formed under 5 atmospheres pressure of CO2.
Malachite under this partial CO2 pressure.
If, and is an *if*, malachite is formed inside the azurite crystals, that means that azurite crystals bottoms are connected to a place where partial CO2 pressure is lower than 5 atmospheres, and water is there. And that azurite crystals cover all access of water inside the vug where crystals are. Which seems to me an oximoron: vug should be connected to anything that lets the pass of water and elements to grow azurite. If vug is sealed, well, how could be azurite (or anything ...) grown?. If it is not sealed, how to avoid the pas from azurite to malachite on surface?

I humbly remember readers that a known German dealer in minerals explained, many years ago, that he bought some malachite stalactites from Kongo that were man made (one broke, and inside was all...copper pipes among other man made niceties....)

Maybe is just as Kevin says, a malachite base covered by an azurite overgrown....
Which in this case would be easier to explain and understand

With best wishes

Lluís
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PostPosted: Jun 04, 2018 09:33    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

Their abstract will be printed later this year in Rocks and Minerals. I hope they have expanded it beyond what is in the program notes.
Yes, they reported your option 1, replacement.
I will quote the abstract and hope not to be violating any rights:
"The surface of almost all azurite to malachite pseudomorphs is to too rough to allow large, thin azurite coatings. Usually the azurites growing on the surface are blocky. A volume reduction is necessary for an internal pseudomorph to form. The reduced volume allows a path for more water introduction and carbon dioxide escape. The reduced volume provides a place for the byproduct malachite without adding internal pressure, which would suppress formation of additional malachite. Internal study of these pseudomorphs produces structures similar to those found in primary malachite crystals. The process is almost entirely internal and the azurite surface transformed last to yield very interesting surface patterns."
If you want more than that, contact John Betts through his web site. All I have for Mr. Straw is an address: 1913 Hackberry Rd. Bloomington, Il 61704
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PostPosted: Jun 06, 2018 16:38    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

just an FYI - I posted the same questions on mindat - see:

https://www.mindat.org/forum.php?read,6,438594,438603#msg-438603

bob
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PostPosted: Mar 06, 2019 20:27    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

At the 2019 TGMS Show in Tucson, I saw the specimen shown below in one of the top-top end dealers booth. To me, this specimen is damaged in about a half dozen places where - I think - the very thin final azurite coating is chipped off the substrata of malachite-after-azurite. I point to the roughness of the interfaces between the thin outer azurite coating and underlying pseudo.

I hope that the dealers has scoped this closely and concluded it is natural - or...caveat emptor.

bob



IMG_1569.JPG
 Mineral: Azurite and Malachite - chipped(?) interface
 Locality:
Milpillas Mine, Cuitaca, Municipio Santa Cruz, Sonora, Mexico
 Description:
 Viewed:  4166 Time(s)

IMG_1569.JPG


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PostPosted: Mar 07, 2019 10:58    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

I presented the paper at the Rochester Mineralogical Symposium last spring showing the internal growth of malachite after azurite.

I have found only one instance of azurite altering to malachite from the surface. The other 99% are internally pseudomorphed (Tsumeb, Morocco, Ajo, Bisbee, and of course Milpillas.

The exposed pseudo continues to grow indicating the presence of copper bearing solutions.
These solutions are probably contributing to the continued growth of the original azurite as well.

I find it very hard to believe that a smooth azurite coating can grow on a very rough malachite pseudomorph.

Pictures that help support any theory on this pseudomorph process would be most welcome.

Best regards,
Ray Straw
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PostPosted: Mar 07, 2019 15:30    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

it will make my day, chipped or not.... Just a dream
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PostPosted: Mar 07, 2019 22:36    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

RayStraw wrote:
I find it very hard to believe that a smooth azurite coating can grow on a very rough malachite pseudomorph.

Pictures that help support any theory on this pseudomorph process would be most welcome.

Best regards,
Ray Straw


Ray - I think this photo (from above in this thread) clearly shows natural growth of azurite on malachite-after-azurite pseudomorph. I have lots of others also. I think it is generally considered that the cause of the rich "electric blue" on these Milpillas specimens (and other localities also) is a thin azurite growth deposited on the original azurite xl after it was pseudo-morphed to malachite. light penetrated the outside thin layer of azurite and is reflected back.

is this what you are looking for? is the above all wrong?

bob



interface 1 of example 3.jpg
 Mineral: Azurite and Malachite - natural interface
 Locality:
Milpillas Mine, Cuitaca, Municipio Santa Cruz, Sonora, Mexico
 Description:
 Viewed:  3893 Time(s)

interface 1 of example 3.jpg


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PostPosted: Aug 04, 2019 09:52    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

Bob:

I have examined the specimen pictured and believe the reflections on top are all remnants of the original azurite crystal because all contain steps parallel to the other relected azurites. The steps between these relected azurites indicate that the original azurite was steped on its faces.
I believe it would be hard to nucleate new azurites on a malachite pseudomorph surface with all in the same orientations to each other.

I would welcome any other interpretation to these azurite remnants.

Ray Straw
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PostPosted: Aug 06, 2019 20:16    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

I agree with the argument that this is not simple epitaxy, but for these to be remnants of a hackly shell of azurite, somehow left behind as the body of the crystal was replaced from within...an unorthodox and a counterintuitive mechanism... requires that the evidence all support that model. The individual azurites appear almost crystallographically oriented...but several features indicate they are secondary to the malachite.

1. If the malachite was replacing an earlier azurite stage, why would the edges and crystal faces around each azurite remain not only unreplaced, but seemingly untouched by malachite replacement? We can't see it all, but it is hard to believe that all the azurite on all its faces would escape being touched.

2. From simple paragenetic cross/cutting relationships it appears that the azurite overlaps and sits higher/above the malachite...indicating it is later and was not there to be replaced by the malachite.

3. Areas of individual crystals that are optically/crystallographically continuous/members of a single larger crystal "colony" are quite common. Sand crystals are one example, as are fluorites that grow on top of heavily coated fluorites that nonetheless have continuity at a very fine scale with the material below/lateral to them are also common. Somehow crystals can grow in lateral continuity over considerable distances and "through" various obstacles that look obvious to us, but that the crystals ignore.

4. If this reflects unreplaced azurite with a hackly multi-faceted crystal surface, why do we not see surfaces like that on unreplaced crystals? I can't claim to have seen all th Milpillas azurites around, but that is not a texture I have seen on a pristine azurite.

I have to agree with Bob that these sure look like an azurite stage growing on/after the malachite pseudomorphed an earlier azurite stage.

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PostPosted: Aug 06, 2019 22:12    Post subject: Re: Milpillas "Electric Blue" Azurites AND Malachites - Natural or Chipped?  

Thank you for your take on this issue.

Ray Straw
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