FMF - Friends of Minerals Forum, discussion and message board

[John S. White]

A friend has asked me if I have ever seen a yellow octahedral fluorite crystal. My sense is that I have, but I cannot remember where I saw it nor where the locality is. Therefore I am posting this query on FMF in the sure knowledge that at least some of our viewers will be able to provide examples and perhaps even photos. I will be eagerly awaiting a flood of responses.

[Jordi Fabre]

I can't remember any yellow octahedral Fluorite, excepting the handmade ones. Hopefully some other FMFer can find some example...

[thehippi]

You can check out this website they have a couple pieces of yellow octahedral fluorite

www jimcolemancrystals com

[Jordi Fabre]

[Riccardo Modanesi]

Hi to everybody!
Jordi, do you remember? You sold me some yellow fluorite from Asturias, though it is cubic and not octaedrical. And what about the crystal you told about in this forum? Do you mean cleavage crystals as I think? Or what do you mean by "handmade"? I submit you this question because I have never seen yet a synthetic fluorite crystal. As a gemologist I mean an "handmade" crystal as a synthetic or artificial material.
Greetings from Italy by Riccardo.

[GneissWare]

[Jordi Fabre]

[Tracy]

I have (had?) a handmade one...

- Tracy

[Tobi]

Loving and collecting fluorite for many years, I have never seen a natural yellow octahedron.

[mmauthner]

I, too, have a yellow fluorite octahedron; a nice one, as they go, from Illinois. Alas, cleaved.
None of the collections I have ever looked after contained yellow octahedral fluorite, only colorless, green, pink/red, and purple. I cannot think of a blue octahedron offhand either.

See you soon!
Mark

[Elise]

[John S. White]

Hi Elise:

The rarity or nonexistance of yellow octahedrons of fluorite may well be due to chemistry as little else appears to make sense. Recall, however that the claim has been made (by Fred Pough and others) that temperature of formation may influence the crystal habit of fluorite. Higher temps are thought to produce octahedrons and at lower temps cubes dominate. I am not sure that I buy into this theory but it may well have some validity. The absence of yellow octahedrons may perhaps be a good research project for someone, but unless fluorite crystals can be grown synthetically, I am not sure that much can be done.

[Duncan Miller]

In my sizable collection of Riemvasmaak fluorites all the yellow crystals are cuboid epitaxial overgrowths on the tips of green octahedra, sometime covering the original green crystal completely. Some of them are very stepped, creating a pseudo-octahedral habit, but none are flat-faced octahedra like the green crystals. As they are later growths, the conditions clearly were different and one suspects cooler, but the trace element content must be different too. On several specimens the yellow cubes are incomplete, as in the attached example, but they are not cleaved. Something on the pre-existing octahedral face must have inhibited epitaxial growth. At least, that is what it looks like to me.

Duncan Milller

[Elise]

Hi,
A lot to think about! This morning I thumbed through the Lithographie issue on fluorite looking at yellow and at octahedral specimens - never the same! Unless you count the yellow fluorite twin on page 75. From the text: each individual in the twin is a "cube-octahedron-dodecahedron combination" (Naica, Mexico). On page 45 in the section on France, there is a statement "Cubes and octahedra tend to be smaller and are found in green and light blue as well as violet and yellow" (Buxieres-les-Mines). Perhaps a source, but maybe only the way the sentence reads. I didn't see anything resembling Duncan's enigmatic specimen (beautiful).
Cheers!
Elise

[Duncan Miller]

Here is another Riemvasmaak example of the partial cuboid yellow overgrowths on green octahedral tips to puzzle over. The green octahedral faces are also covered with small cuboid yellow overgrowths. (I suppose I may get into trouble from some quarters for describing this as 'epitaxial' growth, but it is a different generation of growth with a different colour and habit, so I am at a loss for a better term - and no, I am not trying to resurrect an old argument, just showing that I am aware of it.)
Duncan

[Jordi Fabre]

[Duncan Miller]