Coprolite (dinosaur dung)
Whoever said you can't polish a turd?
That's right, the dinosaurs also 'used the bathroom' and this here's the evidence. Somewhere in southern Utah, near the base of the Henry mountains is said 'bathroom.' At least one potty location where the conditions were ripe to preserve these pseudomorphs from the jurassic era.
Although I've hiked in the Henry's, at the time I didn't know that it was once a dinosaur litter box. Instead, I bought my coprolite from a guy in Sun City who had a whole garage full of cut and polished specimens. While most of it isn't very colorful, it's always a surprise what you'll find inside. I'm told that scientists are able to study the diet of the dinosaur by picking apart these stones. Note that there is nothing biological left after 75+ million years, but the minerals that replaced the biota offer clues by the shapes and patterns left behind.
When I bought a few pounds of the stuff, the guy pointed to some red threads in one slice and suggested hemorrhoids. While I'm not sure that 'roids can detach, I'm certainly not versed enough in proctology to confirm or deny. It made for a good story anyway. He also offered to sell me his entire lapidary shop and coprolite inventory. Obviously retired and full of age, I'm sure he would have made me a great deal. It was a nice thought, but not the right time for me.
Here's more information about coprolite.