Geodes are hollow rock filled with dazzling crystals.

I'm at the American Museum of Natural History in New York City and behind me is an amethyst geode that was formed millions of years ago.

But how?

Geodes are generally formed in one of two ways.

The first way involves molten rock.

As that super hot liquid rock hardens, sometimes gases and water vapor get trapped inside, creating hollows.

Over time, the minerals that were trapped in the cavity begin to grow into the sparkling crystals they are known for.

But geodes can also be formed in sedimentary rock as layers of soil pile up on top of each other over time.

The pressure causes these minerals to be compressed into rock.

Organic material like plants and dead animals decompose, leaving hollow areas.

The rock may seem hard, but tiny holes allow water to seep in.

That water contains minerals which collect in the hollows and form crystals.

If the geode is undisturbed and water continues to seep in, the crystals will continue to grow larger and larger.

So the older the geode, the larger and more beautiful the crystals are.

I don't know about you, but I have always wanted to find a geode.

I don't think any of us are going to find a geode as impressive as this specimen behind us.

But if you want to hunt for geodes, you should look for round rocks.

Round or egg shaped, that are kind of lumpy on the outside.

And you might want to look in places where geodes ar typically found, where there's volcanic ash, limestone, or sometimes in riverbeds.

Happy geode hunting!