Comments (2)

By Mom Unplugged, June 7, 2007 6:55 pm

My 6 year-old daughter is obsessed with rocks. I find rocks in her pockets, in her little purses, in jars on her desk, in her nightstand drawer, and once, even in her bed! She even likes to look at and read books about rocks. I list her favorites below.

We got started on geodes when one of her school book fair books came with a small, uncracked geode. She brought it to school on her “Sharing Day” and cracked it in front of her class, a performance which was, apparently, a big hit with her classmates.

In case you have never encountered one, a geode is a very unimpressive looking rock on the outside, as you can see here:

Geodes form in porous rocks such as limestone or lava. If a hollow cavity exists in the rock, water containing dissolved minerals can seep in through the rock’s pores and crystallize on the inside walls of the cavity. If the crystals do not completely fill the cavity, then a geode is formed. The type of minerals in the water determine what type of crystals form inside the geode.

Geodes are a fun surprise of nature. You can’t know what you will find on the inside of a geode until you break it open!

During our trip to Phoenix we visited the Arizona Science Center. My daughter was very excited to find a large unopened geode in the gift shop. Here it is in its package:

The instructions said to keep it in its bag and bash it with a hammer. Here is my mini-geologist giving it a whack:

Well, it took a lot of banging and I was the one who had to deliver the final, fatal blow. I am not sure we centered our hammering too well (apparently it works MUCH better if you use a chisel first to score a line around the “equator” of the geode - see here for good instructions), but the crystalline interior is clearly visible:

Here is a close up of the surprise contents of our geode in the sunlight. Looks like lots of quartz and chalcedony:

You can find geodes in many science and museum stores, or order small and large geodes online at stores such as The Geode Gallery, The Desert USA Store or Mama’s Minerals.

My 6 year-old daughter’s favorite rock books:

Some good DK Publishing books for older children (9-12):

If you get REALLY into this geode-thing, here is a fascinating-sounding book all about geodes (written for adults, but mini-geologists might enjoy the photos):