FMF - Friends of Minerals Forum, discussion and message board

[Martin Rich]

Very interesting but I think this is not a "pseudomorph" of Pyrite after Pyrite. Anyway it looks very nice!

Martin

[bob kerr]

possibly not a true pseudomorph - but it seems that the cubic form of pyrite was replaced by another crystal form of pyrite.

so what would this be then? what is the visible pyrite crystal form?

hopefully one of our experts can clear this up.

bob

[Michael Shaw]

I have been contemplating this image since I first saw it yesterday, and I had the same impression as Martin. I don't know why you would call this a pseudomorph. The classic definition of a pseudomorph is one mineral replacing another while retaining the crystal form of the mineral being replaced. Perhaps a question of semantics, or maybe not having seen the specimen in person, but to me it looks like the original cubic pyrite crystal has a second generation overgrowth of smaller pyrites with a modified crystal form. I would be very interested to hear Peter Richards weigh in on this one. It's a very nice specimen in any case.

Michael

[Matt_Zukowski]

Looks to me that etching and recrystallization of smaller crystals on the larger crystal could produce this. If so, not a pseudomorph.

[Martin Rich]

Matt, I think you are on the right way. An other possibility is, that a main xl was broken by tectonic forces. A lot of Pyrite crumbles are grown to this smaller crystals as seen on the photograph.

Martin

[marco campos-venuti]

Why not pyrite pseudo after pyrite?
Normal case of pyrite growing above pyrite is that the crystal continues to grow and nothing chance.
When we have epitaxial growths it is because for some reason, the nucleation increases and many small crystals grow oriented above the face of the previous pyrite, as is the case of these pictures (Las Palmas, Peru).
What is the reason for the disorder in the Racracancha crystals? Maybe the original crystal was in an unstable chemical condition and starts to be replaced by, for example, limonite. Before the process was completed, chemical conditions come back and pyrite is stable again, and starts to regrow replacing limonite. Result: pyrite pseudo after pyrite. (or pyrite pseudo after unknown mineral pseudo after pyrite). A little tricky, but realistic.

[Rei]

Wow, that's... unusual.

[prcantos]

I would like to contribute to this interesting thread showing a pyrite crystal from Merelani Hills, Manyara, Tanzania. It is a complex crystal combining pyritohedron, octahedron, cube and trapezohedron (tetragon-trioctahedron) faces.

[Martin Rich]

I want to show an unusual habit of Pyrite. This crystal is extremely elongated. Length: 12 mm, diameter: 0.1 mm, this is a ratio of 1: 120!

Martin

[Josele]

What a weird pyrite! Sorry for my curiosity, don't want be prying but, how was it identified?
The only other photo of pyrite from the same quarry is quite different!

[Martin Rich]

Hello Josele!

The crystal shown in the image is only visual identified. Ok, not very professional! Another, smaller xl was identified by XRD as pyrite and has a thin coating of Fe-oxides. Such elongated pyrite crystals are rare, but not uncommon in (organic material yielding) limestones like in the Zöchling quarry, Lower Austria. Millerite and silicate minerals as well, like Amphiboles, do not occur in this quarry.

Martin

[Jordi Fabre]

Another example of elongated Pyrite (analyzed) from Minas da Panasqueira, Portugal

[Josele]

I wonder which forces act to develop so asymmetrical growth in an isometric mineral.
Definitely crystallography is as complex as it is fascinating.
Thanks for your kind explanations.

[Roger Warin]

Hi,
Epitaxy on the same mineral is a parallel-axis growth. Contamination of the surface can prevent the second orderly growth.
Roger.

[prcantos]

Diploid-shaped pyrite crystals from Duff Quarry. See https://www.mineral-forum.com/message-board/viewtopic.php?p=11208#11208 .