I was talking to my brother the other day. He lives in Pennsylvania, parts of which are quite rich in certain types of fossils. He happened to be looking down in the parking lot at the doctor's office and he noticed rocks containing fossils! He gathered them up and showed his children. His son became very excited as he scanned the parking lot for more, when he noticed a "blue" rock! He started hopping up and down and ran to show his Dad the magnificent find. A blue rock!
Context is everything...The curbs had just been painted, and apparently the crew got sloppy. Pre-painted rocks are great, but not geological marvels!
I happen to know my brother sorted blue pebbles with white lines in them on the car port roof, just so he could make extra wishes, (everyone knows these have magical properties). He also once dragged a very heavy coral colored salt formation, which turned out to be a salt lick, half a mile cause he didn't know what it was, so he should let a curb rock slide. All kinds of weird things are still treasure if you are rock crazy.