FMF - Friends of Minerals Forum, discussion and message board

[Jesse Fisher]

Most of the fluorite we find at the Rogerley Mine is pretty much a uniform green, but occasionally we find crystals that have distinct yellow zones, usually at one corner of the cube. Weardale fluorite is well known for its strong fluorescence under long wave ultra violet light (LWUV), and recently, while examining some such crystals under LWUV I noticed that the fluorescence of the green portions was much stronger than the yellow.

Intrigued by this, I began a survey of crystals from other local mines that showed internal color zonation. While Weardale fluorite does not, for the most part, show the strong internal color variations seen in fluorite from some other locations (notably, Southern Illinois) internal color bands, often in subtle shades of purple are actually fairly common. The most common colors found in fluorite from the region are various shades of purple, green, yellow/amber, and colorless. I found that the purple and green colors are uniformly more strongly fluorescent than the yellow or colorless varieties, and that the intensity of fluorescence varies with the internal color zones. Some photos of this are below.

Fluorite from the Weardale region is known to have elevated levels of a suite of Rare Earth Elements (REEs), and several authors have speculated that this may be the cause of the intense fluorescence, if not some of the the actual colors. As there looks to be a direct correlation between the intensity of fluorescence and the various colors, it would be interesting to see if there is any correlation between REE levels and the internal color variations in some crystals. Unfortunately, I don't have a microprobe in the basement. Anyone know somebody who does?

Cheers,
Jesse

[GneissWare]

[Ru Smith]

Lovely images, Jesse.

[Mark Ost]

Very nice Jesse. I have several pieces from Rogerley and they are very fluorescent, though the ones I have do not show the zoning so well illustrated in your samples. My Mibladen ones do have nice zoning with two color response. Some night I would like to see how far from one of my English samples I can hold the light and still get a visible response. One has such good response I have gotten it to fluoresce with a prism in the UV end of the spectrum coming out the prism. My Clay Center and Tennessee also have fine zoning. Thanks for the nice photos.

[Mark Ost]

Oh do these patterns reflect fluid changes while the crystal is growing?

[Ru Smith]

A Hilton example with faint bands.

[ian jones]

Zoned fluorite from the Weardale area is not uncommon. This Boltsburn piece is particularly strongly zoned.

[Josele]

[Josele]

Only to add that lumuniscence spectroscopy techniques helped to determinate some color centers which act also as luminiscent emission centers, and to recomend a book with exahustive information about this: Luminiscence Spectroscopy of Minerals and Materials, Michael Gaft et al., Springer, 2005.

[Ru Smith]

Excellent information, Josele. Thanks!

[nurbo]

Here are some more Weardale examples, I especially like the first Blue Circle example.

[Jesse Fisher]

I recently acquired a twinned fluorite crystal from the Boltsburn mine that shows remarkably well developed color zoning for North Pennines fluorite. The LWUV image reveals much more detail than is visible in the normal light image.

[Ru Smith]

Beautiful crystal, Jesse.

[colin robinson]

That pinkish colour in the Boltsburn crystal is probably the rarest colour to be found in Weardale fluorites. There was a small outcrop in West Newlandside (long gone) and I've seen it from Cambo but, apart from that, nothing. I'd be interested to see which element is responsible.

[Mike Wood]