FMF - Friends of Minerals Forum, discussion and message board

[Mathias]

Dear FMF friends,

Today I purchased a specimen that came with the following label: "Psilomelane, Brazil".
The vendor said that he actually doesn't know what it is, he got the specimen as one of a large, mainly undocumented, collection. I believe that it isn't psilomelane.

The specimen is approximately 10 cm, I thought it might be Quartz after Aragonite. But looking on internet, I can't find any similar specimen.

Is there anybody who recognizes this mineral?

Thanks,

Mathias

[Mathias]

There's some additional information:

When I point a laserlight on the reddish portions of the specimen, the area lightens up by dispersion of the laser beam. So these portions are opaque.

You wouldn't expect such properties in case of psilomelane or otherwise iron oxides.

Best regards,

Mathias.

[Kevin Conroy]

Hi, I think that this is probably chalcedony after aragonite from Valle de las Plumas, Argentina.

[alfredo]

I agree with Kevin about the ID and the locality.
Nice pseudomorph!

[Roger Warin]

Yes, I think so.
Here is a chacedony covered with limonite psm after barite.