The "Feldspar Effect" - Is This Really a Fluorescent Mineral?
There is something I call the "feldspar effect". When people first start collecting fluorescent minerals in the field they usually are amazed at the typical fluorescence of your average feldspar. As they gain experience and see more fluorescent minerals they realize that typical feldspars have a pretty dim fluorescence and really is not a collectable mineral. Feldspar almost always glows a deep, dull red/magenta. There are exceptions, but rarely. People new to the hobby just don't have the experience with "real fluorescent minerals" - it takes time to learn which minerals are bright and can be included in a mixed display. I have seen pictures of feldspar which rival the fluorescence of tugtupite - impossible.
On Facebook we caught a lot of flack from the "Yoopers" when we tried to explain this problem. They found glowing pebbles of sodalite on the beaches in Michigan which were really not that bright but the photos compete with Greenland sodalite. It's not isolated to yooperlites, but can be any rock collected exclusively by folks new to the hobby without seeing other examples of fluorescence. Lots of rocks glow, but not all are significant fluorescent minerals.
The real problem occurs when folks start taking pictures of these "new finds" without having experienced what a truly collectible fluorescent mineral looks like. I don't completely understand what happens in the human brain, but I have seen it happen so many times that I know it's a phenomenon that causes people to way overexpose their photographs. To me, it is entirely obvious that the photograph is often obscenely overexposed. And it's so easy to tell - look at it under UV light, then compare to the pic on your computer screen. Obvious! But people seem to ignore the real life comparison and post pics anyway. I think it has something to do with experiencing fluorescence for the first time, being excited, seeing all the pics online of Franklin willemite/calcite, and thinking their rock is just as good so they gotta expose the pic to make it look like that.
I recently bought a piece of "Condor Agate" on the Fluorescent Mineral Mart (sister group to the Fluorescent Mineral Group on Facebook). I figured this would be a great "teachable moment". Don't get me wrong - it's a neat white light rock for my collection, but it can barely be considered to be fluorescent. I took a few pics to illustrate. I photographed three rocks as a group - an agate from the Richardson Ranch (right), a piece of vanilla willemite and calcite (upper middle) from Franklin (the world's standard - everyone knows what it looks like and how bright it is), and the Condor Agate (left) that I just received (purchased off the Mart). The pic at the bottom center is copied from the listing on the Mart.
Photo #1 - This was taken with a 30 second exposure to match the exposure of the Condor Agate photo that was posted to the Mineral Mart (bottom photo). I NEVER expose my photos for 30 seconds. Note how the Franklin piece is just an overexposed blob. The Richardson Ranch agate looks pretty nice, but it's really also quite overexposed. The subject in question, the Condor Agate looks pretty close to the original photo taken from the listing. Note the blue background in the original photo - that was a hint that the photo was overexposed, but I didn't realize by how much.
Photo #2 - taken with a 5 second exposure to properly expose the Richardson Ranch agate. Note how the Franklin piece is still overexposed but getting better. The subject in question, the Condor Agate has almost disappeared. Except for the slight overexposure of the willemite in the Franklin piece, this photo is a pretty accurate depiction of the fluorescence of the group.
Photo #3 - taken with a 1 second exposure to properly expose the Franklin piece. The Richardson agate is visible but obviously can't compete with Franklin. The subject in question, the Condor Agate, has disappeared.
Conclusion - this is a pretty agate and will go in my white light collection (which is totally ignored lately). It is not a significant fluorescent mineral and should not be sold as such. Folks new to the hobby need to visit museums if they can, find some friends who have been collecting fluorescent minerals for a while, or join a club. They need exposure to the rocks which may our hobby so satisfying.