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GeneralIs this fluorite fake?

13th Feb 2020 18:57 UTCProdromos Nikolaidis

Hello all,

I have bought this fluorite specimen back in 2015 from a museum gift shop and I regarded it as a natural one. However, last summer in Sainte Marie, I saw lots and lots of similar octahedrons and I was informed by a chinese dealer that these are actually knapped to their form. His specimens though were perfect octahedrons while my specimen isn't: the vertices are not forming a single point (hopefully it is visible at the inserted video).

I thought that this observation proved my specimen to be natural but on the other hand I'm not very knowledgeble in terms of crystallography. Can actually fluorites form such shapes?

If it is possible, can the "manufacturers" cut it in such a way to mimic a natural one? I mean that a perfect octahedron is easy to cut but what about that? Does anyone has similar experience?

Thanks for your help!

13th Feb 2020 19:33 UTCKevin Conroy Manager

It's a cleaved octahedron, not a natural fluorite crystal.

13th Feb 2020 19:36 UTCPaul De Bondt Manager

Kevin is right, not a natural crystal but a cleavage.

13th Feb 2020 21:56 UTCPaul Brandes Manager

Agree.
It's a natural fluorite, but cleaved to an octahedral shape.

14th Feb 2020 17:37 UTCEd Clopton Expert

Fluorite can and does form octahedral crystals, but the faces of cleaved and naturally grown crystals each usually have characteristic features not found on the other.  Look at the faces of the natural crystals in the Fluorite gallery, https//www.mindat.org/gm/1576, and compare with the faces of your octahedron.

Cleavage in mineralogy refers to a tendency of many minerals to split more or less cleanly along natural planes of weakness in the crystal structure and can be a useful identifying characteristic.  In general, cleavage planes coincide with possible crystal faces for the mineral in question.  A particular cleaved crystal did not necessarily show that face--you can cleave an octahedron out of a cubic crystal of fluorite, and you can cleave a cube out of an octahedral crystal of galena--but other crystals of that mineral species could form crystals with faces parallel to the cleavage planes that produced the cleaved form.

15th Feb 2020 09:22 UTCProdromos Nikolaidis

09391790015817585319382.png
What still puzzles me though is why someone would produce by knapping an inperfect octahedron rather than a perfect one. To my mind, it seems much easier to cleave a pefect octahedron than to try to produce an inperfect one. My inserted photo is a screenshot from the video and I'm trying to illustrate how it looks like in its upright position (apologies but I don't have the proper equipment to make a descent photo -- red lines to help outline the shape of the crystal)

15th Feb 2020 09:43 UTCFrank K. Mazdab Manager

I doubt someone purposely tried to cleave an "imperfect" octahedron. They likely just tried to cleave an octahedron, and the really nice resulting ones went into one pile, and the "imperfect" ones went into a different pile. 

You purchased one from pile #2; maybe pile #1 samples weren't even offered at that particular gift shop?

While it can be argued that imperfect ones could be further cleaved to improve their degree of perfection, they would also get smaller each time. And perhaps it was decided that a larger imperfect one can yield a better price than a smaller perfect one?

15th Feb 2020 09:24 UTCProdromos Nikolaidis

01690780015817585806367.png
And here is an example by Rock of a fluorite showing kind of similar shape at the vertex (image - 656875)

15th Feb 2020 14:05 UTCKevin Conroy Manager

An experienced crafter can make an octahedron incredibly quickly, so it's often a matter of quantity over quality.  For what the crafters get for this size it doesn't make sense to take the time to make them perfectly. 

Also take note of the clarity of Rock's fluorite.  These bring a higher price than cloudy ones, so it does make sense to take the time to make them perfectly.

16th Feb 2020 14:27 UTCRolf Luetcke Expert

Seems they also polished down the crystal faces.
I picked one up a few years ago only because it was 50 cents.   They used to sell those by the bucket for very cheap prices.   Still pretty, unless you paid a bunch for it.

17th Feb 2020 16:54 UTCProdromos Nikolaidis

It seems that I must move it then to the "fake and frauds" cabinet...

Thank you all for the feedback!

17th Feb 2020 19:14 UTCFrank K. Mazdab Manager

It's not fake, and it's not a fraud unless it was deceptively sold as having "natural crystal faces" (caveat emptor!)

It's simply a cleavage, and a human took advantage of the 4 intersecting cleavage directions to form it into an octahedron. It's no different than buying a big cleavage of Iceland Spar calcite, another common museum gift shop curiosity, and someone taking advantage of its 3 intersecting cleavage directions to make it look like a nice rhomb.

What I'd like to see, and would even consider buying, is a masterfully-cleaved decent-sized dodecahedron of massive sphalerite. But such an item I've never seen at any mineral show or gift shop. One would think the transparent Spanish material would make an attractively cleaved curio, but maybe dealing with 6 intersecting cleavages is too many to control well?

17th Feb 2020 17:42 UTCKevin Conroy Manager

I wouldn't call it a fake or fraud.  It's a stone that's been shaped by a crafter.  Consider it as a roughly faceted stone.

17th Feb 2020 18:11 UTCDavid Von Bargen Manager

Or consider it as an example of octahedral cleavage in fluorite.
 
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