My family looks forward to getting rocks in our socks each Christmas. Our last name is Stone, so perhaps it’s fitting. As soon as the oldest grandchild became adept with a hammer, we introduced my brother’s four kids to “crack your own geodes.” An outsider might wonder why these dumpy, roundish, bland-colored rocks trigger little shouts of joy when discovered in Christmas stockings. It’s because the kids have learned to recognize their hidden potential: when you whack a geode, it splits open to reveal an airy chamber lined with sparkling crystals.
The ones I recently purchased at a museum gift shop were labeled as “Moroccan geodes.” Morocco’s geodes were formed in basalt—just like our Lake Superior agates. But the photos of basalt in this country at the northern edge of Africa look nothing like the glacier-polished North Shore of Minnesota. The African rock is crumbly and brown from ages of oxidation and weathering without a glacier to scour off the rotten rock. It looks more like the limestones of Iowa—which is another place where geodes are common.
It doesn’t matter if geodes form in basalt or limestone; they always need a cavity in which to grow. The holes in basalt were created when gas bubbles hardened in cooling lava. The holes in the Iowa limestone formed when minerals dissolved and left a hollow space. In either case, over thousands to millions of years, mineral-rich groundwater percolated through the space and precipitated sharp-angled crystals of quartz from the walls of the cavity inward.
Sometimes other minerals will join the mix and expand the color palette. As in agates, these colors occasionally form concentric bands. The difference between agates and geodes is that agates are created when cavities in the rocks are completely filled with patterns of colorful crypto crystalline quartz, while geodes grow visible crystals (not always quartz) into a hollow center.
Tradition calls for emptying everything out of the Christmas stockings, eating a Hershey’s Kiss, or five, and then donning shoes and safety glasses before heading into the cold garage. We rummage through Papa’s work bench for a hammer and chisel and then get cracking!
One by one the kids take turns placing their rough, unassuming geode on the cold concrete of the garage floor and tapping it with a hammer. They are cautious at first, not wanting to smash the treasure to bits. By slowly increasing force, they soon find the sweet spot and crack the rock in half. We always hold our breath at the moment of truth, trying to prepare for the potential of ugly innards. The anticipation never gets old. So far we have not been disappointed. Each geode opens to reveal clear, glittering, crystals.
“Ohhh and Ahhh,” we exclaim before trouping back inside to show Grandma and eat more Hershey’s Kisses.
What’s not to love about a tradition that includes hitting things, the joy of surprise and sparkles all in one?