EDDE said:
what about a black light

?
I had started to do a little research on if using a UV light (not a cheap black light) but a shortwave UV light (common party black lights are longwave)
I got my idea on some reading about arrowhead authentication. something I read said that flint will glow under UV.
below is a copy/paste from part of the description on a UV light for sale on ebay.
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Mineral Lighting & Identification - Opal, Fluorite, Willemite, Calcite, Franklinite, Benitoite, Scheelite, Adamite, Sodalite, Hardystonite, Gypsum, Scapolite, and Zippeite are just a few examples of the various minerals that glow specific, identifiable colors under UV light, making a black light a useful tool for collectors and prospectors alike. **please note that some minerals will only glow under SHORTWAVE UV light. Our light is a LONGWAVE UV light, so please be aware of the difference before ordering.
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It would be interesting to get a cheapo UV light and place it in my flower bed and see if it stands out, then get a shortwave UV light and repeat the test. but I dont feel like spending the 100 bucks or so on a shortwave UV light just so I can "see" if it works