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Identity Helpmohawkite
17th Dec 2009 01:24 UTCReiner Mielke Expert
The difference in toughness is obviously that one has abundant native copper ( arsenic rich) and the other doesn't. Is this significant in any way in terms of the mineralogy of the CuAs minerals in the samples? Is there any correlation between the presence of native copper and the abundance of algodonite vs. domeykite or any other species for that matter? Could #2 be something other than mohawkite, the annabergite and lack of black tarnish have me puzzled ?
17th Dec 2009 12:15 UTCLloyd Van Duzen Expert
you mention tarnishing, this seems to be a characteristic of some copper sulphides. I believe some pyrite shows a silvery surface on fresh fractures then tarnishes in time. pyrites tend to leave a dark streak.
My guess would be some form of pyite. Not all pyrite form cubic crystals. Chalcopyrite is similar but usually has a irridesent colour accosiated with it. Pyrite, chalcopyrite and pyrrohtite are all forms of copper sulphide.
maybe research copper sulphides.
best of luck.
17th Dec 2009 14:42 UTCReiner Mielke Expert
Thanks for your suggestions but the color and tarnishing are wrong for pyrite, cpy or po. Also the reaction to nitric acid is wrong for all of those. The specimens were purchased from dealers labelled as Domeykite and Mohawkite respectively. I am sure that is what they are, just not what the dominant components are. In the case of #1 I am sure copper and domeykite are dominant but #2 has me puzzled.
17th Dec 2009 22:54 UTCLloyd Van Duzen Expert
here's a link from the web, don't know if you have seen it or if it will help you but here it is anyway.
hope this helps.
18th Dec 2009 14:54 UTCReiner Mielke Expert
18th Dec 2009 19:11 UTCPaul Brandes 🌟 Manager
From the looks of your photos, they both appear to be the same mineral. If the dealers had them listed as Domeykite and Mohawkite, they were selling the same mineral as Mohawkite is the local, Keweenaw name for Domeykite since it was predominately found at the Mohawk Mine; however, it was also noted at the Ahmeek, Gratiot, and Seneca Mines. Domeykite in the Keweenaw is a mixture of copper, cobalt, arsenic, and nickel. It can have varying amounts of each element which can give any specimen a unique colouration as well as unique tarnishing effects.
Unfortunately, your photos are a little too close to get a good idea of the rest of the rock/matrix, in my opinion. I would actually like to see the matrix it's in to get a better idea of its identity and origin. As I stated earlier though, they do look like domeykites and definitely not pyrite, chalcopyrite, or any other of the copper sulphides. While pyrite does exist in the Keweenaw, it is a very rare occurrance. The reference you provided from the Mineralogical Society is a great source of information into domeykite and its associated minerals.
Take care, and good luck!! B)
18th Dec 2009 23:25 UTCEd Drown
An interesting description of the copper arsenides found in the Keweenaw can be found in "The Copper Deposits of Michigan" by Butler & Burbank; U S Geological Survey Professional Paper 144 (1929).
The Mineralogical Society of America has the text of the paper hosted on their website.
The table of contents can be found here
The section on mineralogy containing the discussion of the copper arsenides is here
Cheers,
Ed
19th Dec 2009 15:14 UTCReiner Mielke Expert
The section on mineralogy was a great help, just what I needed!
19th Dec 2009 17:43 UTCDonald Vaughn
19th Dec 2009 18:31 UTCBill Baker Barr
Incidentally, Japanese metalworkers use an alloy called kuromi-do (99% Cu, 1% As) in the mokume-gane (wood-grain metal) technique because it works like copper but acquires a black patina that contrasts well against copper, silver and gold. It could be considered an artificial whitneyite.
Cheers, Bill
20th Dec 2009 05:00 UTCScott Sadlocha
I am in the process of rebuilding my primary PC at home, and I am getting ready to do so tonight or tomorrow morning. Barring any issues, I should be back up and running soon, and I would like to post some pictures of the pieces I have, to get some opinions. I do have a picture of the largest of the pieces, but it is not that good. Hopefully it is okay for starters. Any opinions of the composition would be appreciated.
The color is very silver, and the luster is metallic of course (some of the other pieces are more gold colored, and a few exhibit some iridescence). The matrix is a very small part of the piece, and there is a thin band of light green between the two, I am guessing this to be chrysocolla. This piece is about 7cm x 5cm x 5cm and very heavy for its size.
20th Dec 2009 16:14 UTCReiner Mielke Expert
20th Dec 2009 19:25 UTCRob Woodside 🌟 Manager
20th Dec 2009 20:03 UTCPaul Brandes 🌟 Manager
Your explanation of the differences between the three Reiner is spot-on!! (tu)
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Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: April 19, 2024 21:56:25