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My discovery!?

Posted by Norman King  
Norman King March 05, 2013 02:46AM
I recently looked closely at my specimen displaying disc-shaped crystals of chalcopyrite from the Sweetwater mine in Reynolds County, Missouri, hoping to learn how this crystal habit has arisen in pseudo-isometric (tetragonal) symmetry. I still don’t understand the chalcopyrite crystallography, but I observed these green patches (see photos) in several places on my tabular chalcopyrite specimen. Ordinarily, I would consider this a no-brainer occurrence of malachite. Except malachite has not been reported at the Sweetwater mine–at least not in Mindat.

I have two questions (well, maybe two and a half):

1. Does anyone know of reports of malachite occurring at Sweetwater? Or, is there some other mineral there that mimics malachite?

2. Assuming you all agree with my identification, would this merit addition to the list of Sweetwater minerals, in view of the fact I have no analyses? (I am fully aware of how many green copper carbonates, phosphates, etc. there are!)

I’d like to upload this photo to the gallery, and add malachite to the mineral list for that locality, but I wonder how the managers would view this.
open | download - green1b,16.2mm-r.jpg (378.8 KB)
open | download - chalco3d,25.1mm-r.jpg (371.5 KB)
Keith A. Peregrine March 05, 2013 10:22AM
Malachite is a definite possibility. In Adams County, IL geodes containing Chalcopyrite, Malachite is also present as a secondary mineral usually forming on top of the Chalcopyrite.

Rob Woodside March 05, 2013 08:31PM
The dolomite looks a little acid eaten, so I wonder if the specimen wasn't enhanced in acid to get the blue tarnish and then never neutralized to give the green???
Norman King March 05, 2013 10:56PM

You sound like a true skeptic. (Ah, the lessons of experience, right?)

All of the crystals that are broken are golden yellow on the inside but covered with bluish tarnish externally. You can see them in the lower part of photo "chalco3d,25.1mm-r.jpg (371.5 KB)." You can also see in those crystals that the tarnish goes into them a short distance, then fades. A few patches of dolomite are also covered with those spots that look like green chicken-pox.

I acquired the specimen from Dan Weinrich, who sells a lot of Sweetwater mine specimens. He posted one photo (273977) with a child of a specimen that has the tabular crystals but little or no tarnish, if that might help.
Matt Neuzil March 06, 2013 12:10AM
It is odd that the malachite is like "chicken pox". why wouldn't it coat the whole of the crystals? however i imagine that if it was aid treated that perhaps it might not have been the only sweetwater piece to come up with this malachite "virus".

I'm staying with the law. "innocent until proven guilty"

A buena hambre no hay pan duro
Mineralogical Research Company March 06, 2013 12:28AM
Hmmm, I can smell acid from here.... well, almost.

Norman King March 06, 2013 01:10AM
Matt's question, "Why wouldn't it coat the whole of the crystals?" is interesting.

OK, I give--why wouldn't it?

Does that relate to whether it was a natural process or not?

Does that have a bearing on whether it is malachite or not?

I'm not arguing, I'm just wondering. (Like I said, it's an interesting question.)

Another point Matt raised: How many other Sweetwater mine pieces have these spots? I didn't notice them until I spent some time with my specimen under the microscope. Originally I photographed it with my Canon SX10-IS with macro lens here at the house. My photo (photomicrograph) labels above include the field of view for each one. Doing a little measuring on the photos and simple math, I came up with a size range of the spots from about 0.02 to 0.04 mm, or from 25 to 50 per mm. Those would be difficult to see without the microscopic examination, and they might have escaped notice. So, can we ever really answer that last question?
Kelly Nash March 06, 2013 03:48PM
I agree with Matt (innocent until proven guilty). It's not necessary to invoke acid treatment to account for malachite, it's a common weathering product of chalcopyrite, and all that's needed is some circulating groundwater with a little CO2 in it. Missouri DNR reports malachite in lead mines in central and SW Missouri (here: I think Norman's suggestion that they have always been there as sparse tiny green spots is probably more on the mark.

As far as acid treatment to get the blue tarnish, I've seen many pieces with gaudy blue chalcopyrite enncrusting parts of lustrous calcite crystals, I don't really think they're going in an acid bath. I've quizzed Dan myself about whether these irridescent chalcopyrites are chemically treated, and he insists that the miners he knows don't have the time or inclination to do this, and many have seen them in place. Also, I've seen huge, flawless, calcites with very tiny blebs of bright blue chalcopyrite on them. In my opinion, there would have been no reason to treat those specimens in a chemical bath, and risk dinging the calcite crystal tips, just to get a tiny spot of irridescent chalcopyrite on the backside.
Bob Harman March 06, 2013 05:55PM
As KEITH P points out, malachite is indeed found in several Midwest situations. Here is a picture of one of my Indiana geode examples with tiny malachite crystal foci on aragonite on quartz. Steven Rose also pictures tiny malachite splotches on chalcopyrites in an Indiana geode about the middle of page 3 on the "Midwest sedimentary geode" thread. His example looks very much like the original post on this thread. My point is that I think that very small crystals (pseudomorphs ?) of malachite on other minerals from the Sweetwater mine in Missouri is quite possible. CHEERS.........BOB
open | download - DSC02208.JPG (968 KB)
Harold (Hal) Prior March 06, 2013 06:39PM
I have personally observed Malachite on Calcite from Sweetwater Mine. Usually in small quantities and associated with Chalcopyrite. Attached are Calcites with Malachite (Kevin Conroy specimen) from the near by Buick Mine. I have also collected Barite in nearby Washington County with small malachite balls on white barite.
open | download - c4a.jpg (22.4 KB)
Kevin Conroy March 06, 2013 09:17PM
Malachite defintely naturally occurs in several of the Viburnum Trend mines, Sweetwater being one of them. While it's most often more of a stain or thin coating on other minerals it's also found as small blebs like on Hal's calcite.

However, I also know for a fact that some of the miners do treat the chalcopyrites to enhance the color. Some use a diluted mix of Drain-o (or other similar products), some use a diluted mix of vinegar and copper scraps, and others use diluted acid solutions.

So, is the malachite on the pictured chalcopyrite natural or not? I don't know!
Harold (Hal) Prior March 07, 2013 03:24AM
Typical Sweetwater Calcite with what is claimed to be Malachite and Chalcopyrite
open | download - $(KGrHqV,!jUE1JBDr)kcBNhRn8yFz!~~_3.jpg (48.3 KB)
open | download - $(KGrHqR,!loE2EcTM6(-BNhRo!i2m!~~_3.jpg (56.5 KB)
Stephen C. Blyskal March 08, 2013 12:37AM
I've suspected every since the tarnished chalcopyrites started showing up on the market a few years ago that someone was treating them to get that color. I've seen massive chalcopyrite treated and sold as "bornite" or "peacock ore" for many years at rock shops, etc. I wondered because in almost 40 years of acquiring Viburnum Trend specimens I had never run across this color chalcopyrite before. It was always a bright, brassy color on the best specimens. Glad I got my originals early, since I doubt we'll see any untreated specimens anymore. Yes, I've added a few of these to my collection, but don't like the upcharge in prices as a result of making them "prettier".
Bob Harman March 08, 2013 01:38AM
So the natural question now to be asked and, hopefully, answered is: Is much of the bright multicolored chalcopyrite (peacock ore) now on the market natural or doctored/enhanced? And, if much of it has been doctored, how can we tell natural stuff from the doctored stuff?
BTW, at least one high end dealer currently, and over the past couple of years, has been selling many, many examples of these multicolored peacock ore specimens. CHEERS.........BOB
Kevin Conroy March 08, 2013 02:34AM
Steve, there are still many miners who don't treat the chalcopyrites, other than giving them a good cleaning, so you can still find natural ones on the market. These tend have multiple-hued red, blue and/or greenish iridescent crystals on the specimen, with the usual brassy chalcopyrite color at least partially visible on unbroken crystals.

Bob, I think almost all of the extremely brightly colored ones that you see at the shows have been treated. I know of a major wholesaler of minerals who was treating these (starting about 5 years or so ago) after getting them back to his home base from the miners. I don't know if he in particular is still doing it, but it looks like the market is flooded with these colorful chalcopyrites.

The mines of the Viburnum Trend produced, and continue to produce, really outstanding mineral specimens. I used to wholesale and retail these minerals so I made regular trips to see the miners. Since I live in the St Louis area I'm only a few hours away from even the southern-most end of the Trend. I've had some very good naturally iridescent chalcopyrites through the years but even the best of these don't compare in color to the hoard of specimens available now. As far as telling the natural from the enhanced, if it looks unnatural it most likely is.
Stephen C. Blyskal March 08, 2013 04:20PM
I'll have to take some photos of some of the brassy yellow chalcopyrites I've picked up over the years. My best one, a solid mass with no matrix over 6" long, came from Chris Wright, of all people. I got many from Glenn Williams when he used to do shows with Hal Prior in Clear Lake many, many years ago. I will look through my old ones, but off-hand I don't remember seeing any with colors before this latest group of high priced specimens hit the market.
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