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Identity HelpUnknown from Ojuela Mine, Mexico

26th Feb 2012 01:13 UTCRobert Simonoff

This was gotten in Tucson this year. The dealer did not know what the black mineral was, but insisted that it was the matrix and should not be looked at. The only thing on this piece worth looking at is the hemimorphite on the other side. The dealer actually took it and turned it back the "right" way. Well,, it seems pretty nice this way as well - I guess the mineral people in our house are just strange that way.

Anyone have an idea what this might be. It has been suggested that it is a romanechite cast of some iron mineral (goethite possibly). Any additional thoughts?

Thanks

Bob

26th Feb 2012 02:57 UTCRobert Meyer Manager

It could be a cast of some sort. Have you tried a streak test on the black mineral? It would be interesting and potentially diagnostic depending on the color.

Bob

26th Feb 2012 22:42 UTCReiner Mielke Expert

I've seen that before and assumed it was partly dissolved (leached out) botryoids of goethite or hematite. What is left I assumed was some sort of iron oxide, but I guess it could be manganese oxides as well? Never did look into it very closely to try and figure out exactly what it is. Like most collectors I found the crystals on top of it more interesting.

27th Feb 2012 02:48 UTCCraig Mercer

Probably Limonite

27th Feb 2012 04:23 UTCStephanie Martin

Bob - I agree with you, the back sides can be as interesting as the front. I can't count how many times I found the bottom or back sides of thumbnails more interesting than the front, only to be obscurred by that darn tack or worse, glued :-X .

In any case, that sure is a cool "matrix" and reminds me of a piece that Dana Slaughter has in the gallery also from Oujela, with a strange cast like formation. Perhaps Dana might have more insight on your piece and will chime in.

http://www.mindat.org/photo-249399.html