Thursday, October 1, 2009

Cracking Geodes

As I mentioned in an earlier post, I got a lot of ideas from the Homeschool Share unit for the book Rocks in His Head. One idea that I thought sounded fun was to crack open a geode, so I ordered three large (2 inch) geodes from Home Science Tools.

Y'all, it was money well spent.

Give my kids a hammer and the green light to bust away at something, and it's like you've turned them loose in a candy shop.

It took a lot of whacking to crack the geodes open, so there was a good amount of time to see everyone's anticipation build over what might be inside of each one. We made so much noise in our excitement that at one point some neighbor kids came over to see what all the hootin' and hollerin' was about.

Oh, and just in case you're like me, and had never heard of a geode until reading this post, let me fill you in. Geodes are porous rocks that are hollow on the inside. Over time, mineral rich water seeps through the outer layers of the rock and crystallizes in the hollow cavity inside. If the cavity is not completely filled up with crystallized mineral and there is still some hollow space left on the inside, then a geode is formed. Depending on what types of minerals are in the water that seeps in, different types of crystals can form.

On the outside, a geode looks like an ordinary, not-so-unique rock, but there's a treasure on the inside.

If you give this a try, be sure to wear safety goggles and cover your geode with a towel.

Superman's had quartz crystals on the inside.

Future Mineralogist

We're still working on identifying the inside of Sweet Pea's.

Giggly Girl was all business when it came to cracking hers open.

We think the white in the center is quartz and the black is possibly basalt.

If you're looking for a fun, educational gift to add to your child's Christmas list, you can't go wrong with geodes!

You can see the rest of our adventures with Rocks and Minerals here.


  1. What a really nice blog. I have always wanted to do a rock unit with my children.

  2. What I want to know is, where do people find geodes (without ordering them)?? And when you do find one, how do you know it is a geode, and not an ordinary rock?? We live in the desert. There are rocks EVERYWHERE. Could we be living in a geode treasury? My little kids would love this, but after smashing 1,000,000 ordinary rocks to find a geode, I think the excitement would wear off.
    Found you through the Homeschool Carnival. :o)

  3. ebay has a lot of geodes from even better places like Indiana, and Iowa. And most are cheaper and much larger than the ones you bought. I bought a box of Indiana Geodes (24) that were between 8 inches wide to 3 inches wide, and most were hollow with awesome Crystals inside! My kids LOVE geodes! They are a great teaching tool also!
    The white inside that looks like grapes is called Botryoidal! (Greek for grapes I believe)

  4. I'm no expert, but what could be in Sweet Pea's geode is chalcedony (pronounced cal-sidney). It's somewhat wormy to the eye. Small bowl like formations, called chalcedony roses, are quite beautiful, but the ultimate form is what's mistakenly called "fire agate".
    But I could be wrong.


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