On our outing to Penfield Quarry on Saturday we found some pieces of fluorite. A few of the people there said it would glow under a black light. Cool! I used to have black lights when I was a kid, along with the various fuzzy black light posters. I might even have a black light bulb still packed away somewhere, but if I do, I don’t know where it would be.
So I headed out yesterday to buy a black light bulb. I stopped in a Home Depot. They had a 24″ black light bulb, and an 18 inch black light bulb. They were not cheap either. I think the 18 inch bulb was like $12 maybe. Not sure. I looked for a portable fixture that could be plugged into a wall, but didn’t find one, and I didn’t have a lot of time. I looked around some more, and found a 75 watt incadescent black light bulb. And it was only $4. So I bought it and headed out.
When I got home last night, I screwed it into a lamp, and turned it on. I held the fluorite and other rocks under the dim light, and they didn’t seem to noticibly glow at all. We turned off the lights, and still nothing. It was still somewhat light, so we waited till after dark. Again, no glow. Hmmmm…
We thought the light might be too dim, or maybe the incadescent light has the frequency or something.
Today at lunch, I stopped at Lowes. I found the 24 and 18 inch black light bulbs. The 18 bulb was only $9 here. I went in search of a fixture and found them. I found some fluorescent fixtures the plug into the wall. I found one that would fit the 18 inch bulb for $17. But then my buddy whow as with me found a fixture that already came with a black light bulb! We could find the price. But when I took it to the check out, it was only $20. Nice! I bought it.
When I go back to work I searched for information about black lights and rocks. I was surprised to learn there are different black lights. Long wave (UV-A), medium wave (UV-B), and short wave (UV-C). It seems that the black light I bought is likely to be a long wave. And that what I need to make the rocks glow is a short wave black light. A mid wave black light is what they use on CSI to make bodily fluids glow. Hmmm. I did a search of short wave black lights and found they are expensive. Ouch! I will try the light I bought, and if it doesn’t do much, maybe I will return it. Or maybe I will keep it. Maybe long wave black light will work on different rocks. I will have to do more research.
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Added-

I tried the black light when I got home. Unfortunatly the fluorite didn’t glow. It had a slight pruple color to it, but then everything had a slight purple color to it under the light. I think we will need to get a short wave, or medium wave black light. I will comtinue to do reasearch and see if I can find one of these for a reasonable price. I just can’t justify spending hundreds of dollars on a light just to see the rocks glow. There is always the possibility that what we have is not fluorite and the geology students that identified it as fluorite were wrong.
We did get some reaction with the black light from some other rocks. A couple rocks that had a bunch of dolomite on them, had some spots of a dim yellow glow. When we turned the lights on, we didn’t see anything different in those spots.

Posted by Rob in Rockhounding on May 12th, 2008 |