FMF - Friends of Minerals Forum, discussion and message board

[John S. White]

Jordi will gag on this one, but so it goes. Of late there are countless dealers who are selling cabochons and beads of what they call phosphosiderite, some of which have thin veins in it described as cacoxenite. Almost all state that it comes from Chile, but I have not been able to find out anything about the source area and so I am posting this in the hope that someone who sees it will be familiar with the material and its place of origin. Much of it is quite attractive, although there are suggestions that it has to be stabilized with parafin or something like that.

[John S. White]

I just heard from Terry "Skip" Szenics, who knows the minerals of Chile and Peru probably better than anyone, and he states that he has never seen this material in either country. So the mystery continues.

[Jordi Fabre]

[alfredo]

This material has been around for more than a year, as Rob Lavinski was selling cabochons at least as far back as March 2010. The locality then was given as "Brazil" rather than Chile. Luis Menezes stated that he hadn't seen such material in Brazil. The rough rock was available in quantities of a least 100 Kg (as shown in a photo on Mindat by Aaron Savit).

It was also suggested to be heat-treated variscite, as green variscite from Utah had in the past been turned pink by heating it. In that case, the pink material would not be phosphosiderite. I suppose someone needs to sacrifice a chip for XRD.

[lylegordon]

I needed some Phosphosiderite for a reference material for some X-ray spectroscopy work and I came across this thread in my search. I contacted Alfredo Petrov for a piece of phosphosiderite and I also purchased a cabochon on eBay since they were very inexpensive. I ground up both samples. I performed X-ray diffraction on both specimens and I can confirm that they are both phosphosiderite. I also performed Phosphorus K-edge XANES and Iron K-edge EXAFS on the cabochon. The P K-edge XANES matches well with published data (Ellery, D I et al, J Synchrotron Radiat. 2011 March 1; 18(Pt 2): 189–197). The EXAFS fit (dashed lines in the figures) match well to a phosphosiderite model derived from a published crystal structure (Moore P B, American Mineralogist 51 (1966) 168-176).

I can't seem to post links to the plots/data here so please see my post on the mindat forums if you are interested:
https://www.mindat.org/forum.php?read,55,175008,284910#msg-284910