From the outside, a geode often looks like an ordinary rock. Crack it open, however, and you may discover a glittering crystal-lined chamber that has been forming for millions of years. But why are geodes hollow in the first place? Learn how these fascinating formations develop, why crystals grow inside them, and what determines whether they remain hollow or become completely mineral-filled.

There’s something magical about standing at the edge of a great lake. The wind in your hair, waves lapping against the shore, and sunlight glinting off the water — it’s enough to make you pause, breathe, and just be. ... Lake Superior Agates are famous for their rich red, orange, and golden banding, colors created by iron deposits in volcanic rock more than a billion years old. These stones are Minnesota’s official state gemstone, but they can also be found along ...