PotD, 28.2.2012, pyrite

here is the picture...
[www.mindat.org]

How come this pyrite and many others are in that shape? I'm no expert on mineralogy but that doesnt look cubic form to me. Same goes for xls in shape of rectangular prisms that i saw in pegmatites of local granodiorite. could be a form of twinnig?
What are conditions for growth of such xls? are there any crytalic structual changes in such xls? Is there any other element present in pyrite? i saw a lot of pyrite xls with lots of gold in it, but they were the same as pure FeS2.

thanks!


oh... pls move to Education subforum.

[picasaweb.google.si]#



Edited 1 time(s). Last edit at 02/28/2012 12:43PM by Blaž Vičič.

I cannot be sure, but I am tempted to hypothesize that these may be pyrite epitaxic on whiskers of marcasite.
Evidence can be seen from some of the bars showing some zig-zag on the edges. Pyrite forming bars with a range
of morphologies (continuous bars to more blocky bars) were described from quarries of northern Illinois in
"Pyrite and Marcasite from Northern Illinois." R. P. Richards, E. L. Clopton, and J. A. Jaszczak, Mineralogical Record 26, 129-138 (1995).

Cheers,
John

Pyrite can do alot w/ the right motivation, I'd say.
John, I live in N Illinois, how could I get that article? It appears out of print at the minrec site.

Mike

Mike, Please send me a PM and I'll send you an email with a pdf.

Could it be very long rhomb-dodecahedron ? I have seen something like this in garnets, but not so long.
Never seen rhomb-dodecahedron in pyrite either, even though I think it is possible.

Here is a couple of links to similar pyrite crystals

[www.mindat.org]

[www.mindat.org]



Edited 1 time(s). Last edit at 02/29/2012 11:47AM by Marco Barsanti.

Marco,
Those pyrite bars from Italy are wonderful. They also remind me very much of those from Northern Illinois
so I wonder also if they are from epitaxic growth on a marcasite whisker.

I currently don't have digital images of my specimens to post. I'll see if I can remedy that.
John

The "Extra Lapis nr11 Pyrit" (in German) shows pictures of filiform pyrites from Switzerland, USA and Germany.
I have the impression the XX in the POTD are cube+octahedron, with the cube elongated.
Nearly "pure" rombendodecahedrons of pyrite exist, but they are very rare: I have one in my collection and I have seen a second one on Internet. But small faces of it occur rather frequently on octahedrons from Peru, where they bevel the edges.

Hy,

here are some photos of Slovenian samples which are also elongated kubo-octahedrons.


Pyrite twins up to 1 mm, Ljubljana-Golovec tunnel.

Pyrite needles up to 3 mm, Ljubljana-Šentvid tunnel.

Pyrite twin 4 mm, Ljubljana-Šentvid tunnel.

Good luck

Boris



Edited 1 time(s). Last edit at 02/29/2012 08:38PM by Boris Erjavc.

Hello!

I have a Pyrite-x in my collection, what has a diameter of 0.1 mm and a lengh of 10 mm (it's a ratio of 1:100!). I collected this specimen in the Zöchling quarry, Lilienfeld district, Lower Austria, Austria.

I made some x-drawings. On the left, you can see a perfect combination with {100} and {111}. On the right, you can see the same combination but it is elongated in direction of one crystalaxis. It look's like tetragonal but it is cubic! Elongated xx are not uncomon for Pyrite in occurences of limestone. A epitaxy from Pyrite on Marcasite is a possibility. In the most cases there are special growingconditions. I think low temperature and pressure (like in the most cases of limestone) are conditions for this form of Pyrite (please correct me when I'am wrong).

Halite and Fluorite shows also elongated xx, but not so extreme.

Martin