Here it is!
River rock a.k.a. Best Garlic Smasher Ever
The idea came from a cookbook I read in late June - can't remember which chef to attribute for this genius idea, but it honestly works. One good mash to a clove of garlic decimates the skin of the garlic and crushes it so it's almost unnecessary to chop.
This rock came from Boulder Canyon, Colorado. I had Scott and his mom looking with me for a flat, small-ish rock that would fit in the palm of my hand. This one fit the bill perfectly. I am sure there's a rule out there about leaving no trace, taking no rocks or minerals, but I think one small river rock is okay.