Arsenopyrite : FeAsS

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minID: YRU-F0H

Arsenopyrite : FeAsS

This image is copyrighted. Unauthorized reproduction prohibited.
Field of View: 20 mm
Largest Crystal Size: 14 mm

Crystals of arsenopyrite, aggregates in an orderly manner, to replace completely an hexagonal crystal of pyrrhotite. Below, on the left, of the hexagon, there are blacks sphalerite crystals and at the center of that hexagon small crystals of colourless quartz.
Collection and photo of Gianfranco Ciccolini. Nikon D610, bellows, Schneider - Kreuznach 135 mm; f: 5.6. Focal using 8.

This Photo was Mindat.org Photo of the Day - 30th Jun 2016

This photo has been shown 1071 times
Photo added:12th May 2016
Dimensions:3936x2624px (10.33 megapixels)
Date/Time of Photo:23rd Mar 2016 15:01:50
Camera:NIKON D610
Lens:0.0 mm f/0.0
Software:Adobe Photoshop Elements 13.0 (Windows)
Exposure time:1/4s
ISO speed:64

Other Views - click to switch

View Gianfranco Ciccolini's Photos View Arsenopyrite Gallery

Discuss this Photo

PhotosArsenopyrite - Huanzala Mine, Huallanca District, Dos de Mayo Province, Huánuco Department, Peru

30th Jun 2016 14:48 BSTRalph Bottrill Manager

Im not sure about it being a pseudmorph after pyrrhotite, but it certainly is a classic cyclic twin!

30th Jun 2016 15:26 BSTRichard Gunter Expert

Might this be Lollingite? The twin looks closer to a Marcasite-type than an Arsenopyrite-type.

30th Jun 2016 19:49 BSTRob Woodside Manager

So far no Lollingite has been reported from Huanzala and other similar Arseno pseudos after Pyrrhotite are reported:

You can see the remnant pyrrhotite in the upper left of the photo.

30th Jun 2016 23:06 BSTRalph Bottrill Manager

Rob, that one looks more like a pseudomorph as the arsenopyrite crystals are randomly oriented, unlike the POTD. I Cannot think of any true pseudomorphs being a single crystal, twinned or not, but happy to be proved wrong.

30th Jun 2016 23:17 BSTRichard Gunter Expert

Hi Rob:

Have a look at the Marcasite twins described from Nanasivik. It looks almost identical to the crystal placement on the photo. I agree with Ralph that any pseudomorph I have seen is a random aggregate. If it is a non-random overgrowth then another factor is at play. The Nanasivik Pyrite can overgrow a Marcasite twin so possibly Arsenopyrite could as well?

30th Jun 2016 23:50 BSTRalph Bottrill Manager

That is also possible, although arsenopyrite can form similar twins to marcasite, and seems the simplest answer?

1st Jul 2016 00:04 BSTRichard Gunter Expert

Hi Ralph:

I have not seen an arsenopyrite twin look like the photo; though many Marcasite twins do. Is there a relict core in the twin as there appears to be on the crystal below the one in question?

1st Jul 2016 14:37 BSTRob Woodside Manager

Ralph look closely at the photo- click on it. You'll see that the arseno is almost reticulated. It seems to be depositing epitaxially on the pyrrhotite just like the first photo.

The arseno seems to be making an epimorph with the pyrrhotite eventually leaching out.
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