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San Pedro Corralitos unknown
  
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John Betts




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PostPosted: Dec 23, 2021 15:39    Post subject: San Pedro Corralitos unknown  

I acquired an old specimen from San Pedro Corralitos. It is the typical brown gossan coated with yellow-green mimetite microcrystals to 0.3 mm and bluish-black microcrystals in botryoidal aggregates to 0.5 mm.

The bluish-black mineral was tentatively identified as goethite by the seller. But I have my doubts. The bluish color would be unusual for goethite.And the streak color is distinctly black, not the brown/ochre usually associated with goethite.

Any ideas for possible species that would be associated with mimetite from Mexico?



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PostPosted: Dec 23, 2021 15:40    Post subject: Re: San Pedro Corralitos unknown  

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lluis




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PostPosted: Dec 23, 2021 15:44    Post subject: Re: San Pedro Corralitos unknown  

Maybe just any (maybe mix) manganese oxide?

With best wishes

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PostPosted: Dec 23, 2021 15:46    Post subject: Re: San Pedro Corralitos unknown  

Descloisite and/or Mottramite are good guesses. Los Lamentos had similar only after wiulfenite mainly..

this is a Peter Megaw problem.

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PostPosted: Dec 23, 2021 15:55    Post subject: Re: San Pedro Corralitos unknown  

Mottramite was a good suggestion, but I just checked for reaction to HCL. No reaction which rules out mottramite. Additionally mottramite does not have a black streak.
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Pete Richards
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PostPosted: Dec 23, 2021 16:20    Post subject: Re: San Pedro Corralitos unknown  

Asked in ignorance: what about plattnerite?
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PostPosted: Dec 23, 2021 16:28    Post subject: Re: San Pedro Corralitos unknown  

John...I'm going to go along with Lluis...probably a manganese oxide, given the amount of zinc around likely chalcophanite...it is very common at Santa Eulalia and Ojuela and often has that quasi bluish metallic lustre/color.

Pete's suggestion of plattnerite could be solved under the scope with strong back lighting looking for red internal reflections...but it doesn't quite look right

Cheers AND MERRY CHRISTMAS TO ALL

Peter

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John Betts




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PostPosted: Dec 23, 2021 16:38    Post subject: Re: San Pedro Corralitos unknown  

Pete Richards wrote:
....what about plattnerite?


Good suggestion Pete. Thanks.

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PostPosted: Dec 23, 2021 16:51    Post subject: Re: San Pedro Corralitos unknown  

Under the scope the botryoidal formations show they are brown internally (goethite), but have an overgrowth of blue-black micro-microcrystals (too small to see any details).

I'll just stick with "Goethite" Thank you all.

Best wishes for a merry Christmas!

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