FMF - Friends of Minerals Forum, discussion and message board

[mmauthner]

OK, many months down the line, but I finally located an old image of a pyrite pseudomorph after pyrrhotite from the Nanisivik mine. Unfortunately, I took this with a Nikon 990 over ten years ago, of course in jpg format, which has had years of compression artifacts added. Second, the specimen has since gone to its next mineralogical life as a pile of rubble and sulphuric acid.
Note that this is unequivocally a "pyrrhotite" habit and could not be mistaken for a twinned marcasite. The pyrite after marcasite pseudomorphs I find hard to imagine as being confused with pyrite after pyrrhotite as the angles are quite a bit different. Pyrrhotite rosettes are hexagonal with axis angles at 60 degrees from one another; twinned marcasite looks more like "fivelings" (never complete; usually only up to three axes showing) with axes at 75 degrees to one another.

Cheers,
Mark

[Jordi Fabre]

Not exactly Pyrite after Pyrrhotite but quite interesting, I believe. It is from Turt, Satu Mare, Rumania where other Pyrites after Pyrrhotite appeared in the past.

[Peter Megaw]

Mark and Jordi...glad to see the thread is alive...thanks for both pictures.

Mark, I agree these are clearly ex-pyrrhotite...and on peripheral note I am not surprised they have disintegrated, from what I've seen, the thin platy habit of both pyrrhotite and py ps po seem quite a bit more prone to alter than more elongate crystals.

Jordi, are there any places you can see how far the chalcopyrite has "eaten" into the pyrrhotite and/or is there any residual pyrrhotite left? a magnet can tell.

Satu Mare seems to be fit very nicely with the long-lived, multi-stage genesis hypothesis, which is also exemplified by multple pseudomorphing relationships. Northstar Minerals website is worth a look on this...multiple photographs of elegant pseudomorphs (This is not intended as a plug for Ross...although he deserves it...just a recommendation to check out his pictures)

[Jordi Fabre]