Vivi, my little scientist, today received her Scholastic book order: eight rocks and a little book of experiments to do with them. She’s fascinated. We did a few of the experiments, and will do more after getting some supplies (do people really keep Epsom salts on hand?), but the best thing we did tonight was to start growing crystals on a "popcorn rock" submerged in white vinegar. We should start start seeing aragonite crystals within a few days, but we were impressed by the bubbling and cloud of matter rising up from the rock. Geochemistry for the win!