A mystified reader from Mississippi sent this photo of a large streambed boulder; he'd never seen anything like it. Very few Mississippians have, because such a thing is found only in the farthest northeastern corner of the state. It's Devonian chert, a rarity in this state of much younger mudstones.
Your own neighborhood may be nothing but chert; it's certainly common where I live. But it's always good to be reminded that everything in the world is marvelous to somebody. And I ended up discovering an excellent booklet, "Windows into Mississippi's Geologic Past," published by the state geological agency.