Sunday, August 22, 2010

Garnets

School starts tomorrow, and Peter begged and begged to spend his last day of summer hunting for garnets. Finally I relented and we headed off to Trolla where my geologist friend Allan had sent us a couple of years ago to find these interesting crystals.

Rather than hunt for the stones near the road (dangerous) we headed down to the beach, and this little voyage turned into an adventure. First we met moon jellies and a fish head. Then we had to cross a seaweedy section of beach and risk meeting sea monsters. Past the seaweed were countless snails. Finally, we were rewarded with big boulders of garnet rich rock.

Oh, the happy mining that followed. We broke open stones with hammers and the small red crystals popped right out. Some of the pieces of stone were soft enough that we could break them with our fingers. And we found a few pockets of pulverized stone that we could sift through and find loose garnets just waiting to be collected. Most of the stones were tiny, but we found about a dozen that were about the size of baked beans.

These stones are mathematically very interesting. The shape is called a rhombic dodecahedron because it has 12 identical faces that are rhombuses. The diagonals of each rhombus measure in the ratio of 1:√2. If draw lines to highlight the shorter diagonals, you'll see the lines form a cube. If you draw lines to highlight the longer diagonals, they'll form a regular octahedron. Mmmm... a yummy shape. And rhombic dodecahedrons pack together tightly to fill space. Not many polyhedra will do that.

We got out of there just before it started raining, and brought several rocks back home with us. The kids continued smashing rocks on the porch for about an hour when we got home. It was the perfect way to spend the last few hours of summer.

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