Shortly after my family and I moved to Bloomington, Indiana, three years ago, my six-year-old son invited a neighbor boy over to play. The neighbor asked if they could go geode hunting in the wooded creek behind our house. I did not know what geodes were or what kind of artillery might be required to hunt them, but I sent the boys out with my blessing, hoping they could not get into too much trouble. A little while later, I saw them staggering out of the woods, splattered with mud and clay. They were carrying a heavy rounded rock, which they dumped unceremoniously on the porch.