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Improving Mindat.orgPyrite ?

7th Jan 2019 06:19 UTCGiuliano Bettini

I submitted this one

https://www.mindat.org/photo-930012.html

as 'marcasite' but Mindat changed it: pyrite, user gallery only.

This, enlarged, doesn't seem cubic to me but instead orthorhombic

FoV: 1.5 mm.

Here are some other crystals of the same specimen:

FoV: 7 mm.

Thanks,

Giuliano.

7th Jan 2019 06:33 UTCKeith Compton 🌟 Manager

To me it looks like stacked Chalcopyrite.

7th Jan 2019 07:21 UTCErik Vercammen Expert

Pyrite: octahedron truncated by a small face of the cube.

7th Jan 2019 10:32 UTCGiuliano Bettini

Thanks Erik,

cube, octahedron... you see, reminded me of the marcasite from Casciana, Tuscany, here the paper by Paolo Orlandi, and an image, too

http://www.stsn.it/images/pdf/serA110/06%20Orlandi.pdf

The specimens from there are similar.

7th Jan 2019 18:48 UTCMichael Sommers

While I do not profess any sort of expertise on the subject, my initial reaction would be to question whether the images from that paper in B, C (copied above) and E are in fact marcasite. To my eye, they look like isometric crystals, not orthorhombic.

7th Jan 2019 19:29 UTCReiner Mielke Expert

I can see where C could be orthorhombic because I do not see modifications on all the corners which suggests a rhombic dipyramid modified by a prism rather than an octahedron modified by a cube. However in your sample I see no evidence of this. A simple nitric acid solubility test will tell the difference as marcasite will leave behind a residue of sulphur whereas pyrite does not. See this: https://www.mindat.org/forum.php?file,11,file=48275,filename=Marcasite_Test.jpg and this https://www.mindat.org/forum.php?file,11,file=48276,filename=Marcasite_Test_002.jpg

7th Jan 2019 20:57 UTCEd Clopton 🌟 Expert

Asymmetrical absence or presence of modifying faces is not diagnostic--maybe it indicates the forms that are involved, as Reiner suggests, and maybe it is just random variation in an octahedron with cube modifications as Erik suggests. From the photos, Giuliano's specimens look to me like pyrite.

I agree with Michael that specimens B and C in Orlandi et al. also look like pyrite. Specimen E might be marcasite growing epitactically on the left side of a pyrite crystal.

8th Jan 2019 12:15 UTCUwe Kolitsch Manager

Typical pyrite cuboctahedra.

10th Jan 2019 06:25 UTCHerwig Pelckmans

Reiner,

That is some good info. Did not know about that test. Will surely give it a try with some test specimens!

Thanks for educating us!

Giuliano,

Take a close look at the surfaces of the pyrite/marcasite crystals on the Orlandi photos.

The marcasites have really smooth surfaces, and striations are clearly visible.

Not so for B and C. The crystal habit sure looks like octahedron modified by small cube faces. Typical for pyrite.

So I assume it is pyrite.

I wonder if the researchers did more than just an EDX and looking at the photos to come to those IDs.
Is that mentioned in the text, Giuliano?

It would not be the first recent scientific paper with such errors.

Your specimen, Giuliano, looks like a typical pyrite specimen, as stated above.

Cheers, Herwig

MKA (Min Soc Antwerp, Belgium)

11th Jan 2019 10:33 UTCGiuliano Bettini

@Herwig

Thank you. I can not find the answer to your question in the paper

@All

Thank you all. I will try to get an analysis in the future.

Giuliano.

16th Jan 2019 10:23 UTCGiuliano Bettini

Hi all!

The Orlandi’s paper mainly describes this locality here:

https://www.mindat.org/loc-130633.html

On the same site I collected some specimens in the 90s.

For sake of completeness I've published some photo here:

https://www.mindat.org/article.php/2921/My+specimens+from+Casciana+Terme+%28Era+Valley%2C+Tuscany%29

Thanks,

Giuliano.

16th Jan 2019 10:46 UTCPaul De Bondt Manager

Hi Guiliano,

Thank you, but the pictures you uploaded today seems to be uploaded in an inappropriate way.

Look at the header, all are like this : https://www.mindat.org/photo-932490.html and the title is Casciana.

Please look and correct. Thank you.

16th Jan 2019 11:00 UTCGiuliano Bettini

Hi Paul, there has been a discussion, pyrite? marcasite? so I put just the dimensions of each photo, and I named them Casciana 1 / 2/ etc up to 12. Thanks, Giuliano.

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