When I took a college course about dinosaurs a few years ago, I took the opportunity to confirm what a family member told me when I was very young. Someone had given me a small lump of irregularly-shaped rock and said it was a dinosaur bone. It certainly looked like some kind of fossil, and in 2003 I brought it to my professor to see if he knew what it was.
If my professor was sure of anything, it was that my specimen was not a fossil. It looked like a bone, sure, but it was just a small rock that had formed in a way that looked bone-like. It did not have the honeycomb-like internal structure that is a tell-tale sign of fossilized bone. Such mistakes are easily made, though, and it seems that a similar fossil-like rock has been making a bit of news lately.
This past weekend, DL-Online posted a story about a "baby dinosaur" skull discovered by Minnesota rockhound Mitchell Voss. Held the right way there is something dinosaur-like about the image on the rock, but this resemblance appears to be due to irregular swirls on the rock. This is similar to the famous (and now lost forever)