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If I understand this answer and this comment correctly, minerals like calcite, fluorite, and apatite are "commonly associated with (Rare Earth Element) REE deposits", and like some REEs also fluoresce when exposed to UV light. But the intrinsic fluorescent properties of those minerals are not caused by REEs.

Is this just a pleasant coincidence; the presence of one fluorescent mineral is often associated with the presence of another fluorescent mineral even though their fluorescence mechanisms are different?

Or do minerals like calcite, fluorite, and apatite tend to fluoresce because they contain REEs, thus observation of their fluorescence is a direct indicator of the presence of REEs? Or do REEs only modify the color of their fluorescence, but not necessarily cause it?

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    $\begingroup$ From this webpage. "Fluorescence usually occurs when specific impurities known as "activators" are present within the mineral. These activators are typically cations of metals such as: tungsten, molybdenum, lead, boron, titanium, manganese, uranium, and chromium. Rare earth elements such as europium, terbium, dysprosium, and yttrium are also known to contribute to the fluorescence phenomenon. Fluorescence can also be caused by crystal structural defects or organic impurities." $\endgroup$
    – user18590
    Commented Jan 31, 2020 at 10:22

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The answer to your question is probably the second:

Or do REEs only modify the color of their fluorescence, but not necessarily cause it?

I will give an example of apatite. Here's a cathodoluminescence (luminescence excited by electrons) energy spectrum of a natural apatite. Source.

enter image description here

You can see several different rare earths triggering the luminescence, but there's also manganese. Apatites from granites usually have lots of manganese, and very little rare earths. So their luminescence would be dominated by the 2.1 eV range, which would be yellow. In contrast, apatite from REE deposits would be dominated by Ce, giving a blue-violet colour. They will also have lots of Nd, but that does not help us because it's in the infra-red range.

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  • $\begingroup$ Somehow I missed the notification for this answer, this is beautiful, both graphically and as a multiparameter fit. I'd heard of cathodoluminesence used in semiconductor device analysis but have never seen it used in minerology(?) I'll try to grab a copy of this paper and have a look. Thanks! $\endgroup$
    – uhoh
    Commented Jan 15, 2021 at 23:52
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No it is not by chance. As an ion, rare-Earth metals and compounds behave like alkaline Earth metals, so they form near each other. For example, neodymium has similar chemical properties to barium. They can both modify and cause fluorescence in calcite and/or fluorite.

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