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The NPR.org news article and podcast Greenland Is Not For Sale. But It Has The Rare Earth Minerals America Wants is interesting, and it includes a few large GIFs (too large to post here) that appear to show a UV light being waved over some rocks (not really in the dark) and bright red spots lighting up indicating the presence of some mineral containing a rare Earth element.

Compounds containing rare Earth's including oxides have strong transitions in the visible and infrared and some will fluoresce with visible light. When you read what I type over the internet the signal has probably been amplified dozens of times by erbium-doped silica fiber optic amplifiers at the bottom of the ocean (and everywhere else) and those are likely pumped by Nd:YAG lasers (neodymium-doped yttrium aluminum garnet).

But are UV lights really able to so easily find rare Earth-containing rocks on the ground in Iceland, or are these GIFs slightly gratuitous?

Question: Can I just walk around Greenland with a UV light and find rare Earth minerals on the ground?

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    $\begingroup$ web.mit.edu/12.000/www/m2016/finalwebsite/solutions/… is just a google result and probably not very helpful, but suggests that the rare earth mineral deposits in Greenland are concentrated in only 3 locations. In particular, these locations are on the coast. $\endgroup$ – user967 Nov 24 '19 at 16:10
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I think the answer to your question have to be no.

Lots of minerals are fluorescent in UV light,You can take a look here https://geology.com/articles/fluorescent-minerals/

So as you can see in the linked summary of fluorescent minerals it can be hard to tell what you have found unless you know what to look for.

A better way to find Rare Earth Elements might be to use a Geigercounter,Many of the Rare Earth Elements can be found toghether with radioactive minerals.

Here is an example from Norway https://reeminerals.no/fens-field this is an area not far from where i live.

As you can see in the linked article this area can be seen using detectors from an airplane,Maybe not to tell the composition but it can give a hint about where to look.

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    $\begingroup$ Thanks for your answer, I'm enjoying your links as well. $\endgroup$ – uhoh Nov 26 '19 at 11:09
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Yes, definitely.

In general, REE minerals tend to be fluorescent. In our lab we deal a lot with REE and we have a UV lamp just for fun, to see the colours. Other minerals that are commonly associated with REE deposits are also fluorescent, with the best example being calcite, fluorite, and apatite.

The fluorescent properties of REE-bearing solid state compounds (i.e., REE minerals) are exactly the reason why they're so commonly used in phosphors.

Greenland, in particular, is the best way in the world for that. Because it is glaciated, rock surfaces are freshly exposed with very little alteration or development of soil that will hide the REE minerals.

Whether this is an effective exploration method is debatable, but it is definitely part of the toolbox of any exploration geologist working on REE deposits. And it looks really cool.

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