Improving Mindat.org : Olmiite versus Poldervaartite (original) (raw)

For your information I can tell you that during last year we microprobed more than

15 specimens from N'Chwaning II and Wessels and ALL of them independently

of habit, colour etc. - all turned out to be olmiites with very clear dominance of Mn over Ca in the second position.

Now I have a strong suggestion that all the poldervaartites that filled the mineral market (including all pictured on mindat) are in fact olmiites.

It needs to be said that even the analysis given by the authors of poldervaartite for the homogenous grain of holotype material showed dominance of Mn over Ca.

Only one crystal of holotype poldervaartite used to make a crystal structure showed,

according to authors, slight dominance of Ca over Mn. So actually it seems that

even the holotype poldervaartite is, in fact, the zonal growths of poldervaartite/olmiite.

In our analyses we unfortunately never found traces of such zonal growths, never even a ratio

close to 50/50, everytime Mn was strongly dominant. One thing is evident: it is impossible to clearly ID the species basing on visual examination.

I discussed this problem several times with Renato Pagano (co-author of Olmiite), also with Dr.Bruce Cairncross etc. Renato said that more investigations are needed.

So far, I suggest poldervaartite being EXTREMELY rare species. I certainly don't have it in my systematic collection. Since SA mines are very prolific we can only hope that new find of Ca-rich material will be made, but so far, very tough WDS-work and very BIG luck are necessary to find points of the true poldervaartite!

Warmest,

Anatoly