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Black unknown with murdochite from Ojuela mine.

Posted by Brent Thorne  
Brent Thorne February 27, 2012 11:53PM
Attached is a photo of a some black prismatic crystals that occur on rosasite with murdochite. Are these just elongated murdochite? or something else. Any help would be appreciated.
open | download - unk. black Ojuela mine Mexico 2-27-12.JPG (112.9 KB)
Ronald John Gyllenhammer February 28, 2012 01:44AM
Hi Brent,

I dont think this is Murdochite. These "black prismatic crystals" appear brassy in the image, an effect of the lighting I suppose or perhaps a minor coating of iridescent limonite? At any event, they remind me of Plattnerite. One visable termination looks tapered as with Plattnerite. Also it sort of looks like there's a penetration twin there, much like Plattnerite often shows. Good luck with it Brent.

Uwe Kolitsch February 28, 2012 03:05PM
Brent Thorne February 28, 2012 03:57PM
Thank-you for the suggestions. I considered delafossite, but I can not see a trigonal crystal form in these crystals. I believe that plattnerite is probably the correct mineral. I noticed a similar specimen of plattnerite on rosasite listed in the Mindat gallery for the Ojuela mine.
A couple of other observations. Part of the matrix is tenorite and cuprite. Also, many of the crystals have penetration twinning at 90 degrees to each other.

Edited 1 time(s). Last edit at 02/28/2012 07:13PM by Brent Thorne.
Lefteris Rantos February 28, 2012 10:01PM
That's interesting... Plattnerite is not supposed to form twins at right angles. Being isostructural with Rutile, it forms typical "knee-join" twins at 120 degrees, just like Rutile xls. See for example

I don't know about the orthorhombic dimorph of Plattnerite, Scrutinyite. Does anybody know if it could form twins at 90 degrees?

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