Iowa's state rock, the geode, illustrates the adage that 'you can't judge a book by its cover,” said Marv Houg, president of the Cedar Valley Rocks and Minerals Society. 'It's a great teaching tool ...

Crack open an unassuming stone, and you might just uncover a little conclave of crystals within. Their walls are glittering with quartz, amethyst, or calcite, protected by a hard shell that was shaped ...