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Identity HelpBlack unknown with murdochite from Ojuela mine.

27th Feb 2012 23:53 UTCBrent Thorne Expert

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.

Brent

28th Feb 2012 01:44 UTCRonald John Gyllenhammer Expert

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.

Ron

28th Feb 2012 15:05 UTCUwe Kolitsch Manager

Delafossite?

28th Feb 2012 15:57 UTCBrent Thorne Expert

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.

Brent

28th Feb 2012 22:01 UTCLefteris Rantos Expert

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 http://www.mindat.org/photo-14494.html

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

Lefteris.