These fluorescent rocks abound on the shores of Lake Superior

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We used a blacklight and found a surprising number of our rocks about the house fluoresced. Get a cheap blacklight flashlight (be careful, UV is bad for you), a visible light bandpass filter, and explore!

We are planning on going to the lakes to look once things get safer, this sounds like a fun rockhounding weekend to us. :slight_smile:

(Note: while not ideal and somewhat substandard, there are much cheaper flashlights emitting the right wavelengths available than the fine flashlights that are ideally suited for the activity sold for rockhounding. Don’t let not wanting to spend $100 on a flashlight stop you, we got ours on Amazon for under $10, and filters for under $10 on ebay. They aren’t as good, but rocks still fluoresce under them!)


Agates are fairly common on the Lake Superior beach too. Lake Michigan has Petoskey Stones. I got pretty good at finding them when I was a kid.


I’m pretty sure Julian May wrote an excellent article based on these. See here.

I really want to go back to around Duluth and look for rocks again. I had been there almost a week before I found out what awesome rocks they have. Like lots of agates.

I started that way too. I found some weakly fluorescing rocks in decorative rocks around my inlaws house.

If you go you might still try to get a cheap Shortwave UV lamp. Black lights are long wave and some rocks only glow or glow better under shortwave.

Though black lights are a good place to start. With it being Halloween soon, check the local stores. I found a portable ~6" battery powered UV lamp at Target one year for like $5. The batter pack tabs have broken, but I fixed it with tape.

I have been reposting this a lot lately.


Oh that is a really cool thread! :slight_smile:

We were kind of staying away from the shortwave UV, but yeah… I think one is in our near future. :slight_smile:

The Yuperlite is weird in that it really likes the 365nm wavelength; we live kind of near the lakes, so when we found out about this rock specifically, it seemed like a good rockhound trip we could do once the summer crowds recede in the fall; we kind of geared up for it, now all we need to do is get the RV fixed.

But we did run around the house one night shining the light on all the rocks to see what lit up… that was a whole lot of fun, based on that thread I bet you know exactly what I mean. :slight_smile:


They’re a lot harder to find these days than they were 50 or so years ago. Tourist have taken home most of the nicer specimens of that particular fossilized coral.


There are all sorts of fluorescent minerals all over the place.

It’s a pretty popular lapidary subculture to collect the various varieties.

Try this in your backyard in Texas and you may learn a lesson you didn’t want to learn about the prevalence of scorpions.


One of my favorite things as a kid was that a short cut to my dad’s office went through the geology building, where there was a display case with a black light for seeing cool glowing rocks. Had to stop every time.

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Black light lamps (also called Wood’s lamps) are totally safe as they emit UV-A radiation, which is harmless both for the skin and the eye, although being mostly invisible, it will cause fatigue if looked at in the dark for long time. UV-C lamps are the most dangerous and require proper protection. They’re mostly used as germicidal lamps, and in the past also as EPROM memory chips erasers.


If you’re on the east coast, there’s a tin mine in Ogdensburg, New Jersey that you can tour. The walls of the mine are fluorescent as well as many foundations of homes in the area. Cool trip if your into rocks and stuff.

I have one that I use to hopefully sterilize a room after a patient has been in it, bought after covid. I don’t know how well it works on viral particles, curious if a half potato in the UV room will keep better than in a room without it. Not relying on it, just utilizing the general principle of having both belt and suspenders. Came with no switch, just a remote control, with a timer, so I can turn it on from outside the room. LED. I suppose I could use it with a cardboard cone to shield me, to shine on rocks.

If that’s a germicidal UV-C lamp, then yes, it works for sterilizing objects and surgical instruments, but the item to be sterilized must be entirely covered by UV radiation, which requires tools to be rotated a couple times between exposures. This also makes environment sterilization harder because of objects blocking the UV radiation (which travels as normal light although we cannot see it).
I wouldn’t feel that safe with the remote alone, especially if it’s a cheap general purpose one, whose frequency and codes could match someone’s garage opener in vicinity. It’s an extremely unlikely scenario but I’d put a safety switch in between anyway to keep it off when there’s people in the room, just for added safety.

Good point. Unplugging it should work too. It’s unclear how effective it is, but using it as I hope it damages aerosolized coronavirus.

Always shake out your shoes!

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