These beautiful geodes are made of Pure Bismuth. Bismuth is one of the few materials that have a greater density as a liquid than as a solid. Only a few other materials such as water, gallium and germanium, exhibit this property. The trigonal crystal structure accounts for the cubic formations. The iridescent rainbows of colors observed are caused by light scattering off thin layers of bismuth oxide formed when the surface of the hot bismuth reacts with the air. These geodes measure roughly 4" in diamater Great for teaching about crystals, states of matter or even as a gift!
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