local hand specimen

I'm not approached to identify rocks very often. Most of the time I'm working in the field, I'm not in a location that's visible to the public, and when I am, I'm usually not doing something that obviously involves rocks. That's fine because rocks aren't actually my thing.

A while back, a maintenance guy working on one of my sites noticed that my business card had a variant of the word "geologist" on it. He mentioned that he lived in an old house, and that while they were renovating it, he found a funny rock tucked behind a wall. Could he bring it in for identification?

I expected him to bring in a piece of slag (often confused for rock around here, and in some places, much easier to find than bedrock), or maybe a rock with some reasonably large chunks of mica.

What he actually brought me was a fist-sized, perfectly formed crystal that I could have used as a type example for a mineralogy class. It also happened to be rare enough that I could give him a short list of local mines that it most likely came from. I'm not going to show the actual mineral here because it was so locally specific, but picture something like this (from here):

(Franklinite, pictured above, is a tad more rare than the mineral I identified, but you get the point)

So I got to tell him that his "funny rock" was actually a historically and geologically valuable specimen, and that with a bit more research (mine years of operation vs. house renovation/build years), he may be able to ferret out a very small list of places it actually came from. He could sell it for a reasonably high price, but I hope he holds onto it - it would make a great family/house heirloom.