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[Roger Warin]

Fluorite – Mercedes-Benz Star

Good tools allowed me to take a good photo of this Mercedes star included in a fluorite crystal from Seilles (Huy-Belgium).
The crystals of fluorite are sometimes large, up to 20 cm on a side.
However, the faces of octahedrons are very often corroded, by a dissolution process, I think.
Beautiful gems have been cut from this material and that of Dr André Rostenne † can be found at the National Museum of Natural Sciences in Luxembourg.
Many poorly formed specimens were cleaved by amateurs and André had given me a few cleavages.
These were made to highlight a star or triangular cross whose symmetry reveals the position of the ternary axis of the fluorite.
For a long time, I had hypothesized that this star highlighted the edges of the dodecahedron. But obviously without being able to prove it.
This fairly clear photo would perhaps provide proof of this hypothesis.
In fact, the branches of the star are triangular, which I had not observed before taking the photo.
My question to you, particularly Pete, are these triangles compatible with section (111) of the dodecahedron?

We can also notice that at the end of crystallization, the content of cations giving the color has reduced, to the point of allowing pure CaF2 to crystallize. Then the last little star appeared with a purple hue induced another additional impurity.
Hydrothermal waters are in motion and can become depleted and then supplied with CaF2 and other cations.

[Bob Morgan]

The purple shape appears to be hexoctahedral in nature, having three pairs of isosceles triangles centered around a triangular shape. You've definitely found the tri-fold axis of the cleaved octahedral face.

[Bob Carnein]

Roger, This doesn't answer your question, but I wondered whether this fluorite (like some of the purple fluorite from this locality) fluoresces red?

[Pete Richards]