The life of a Geode starts humble, as a pocket of air in magma not to deep beneath the earths crust. As the magma begins to cool, minerals get trapped in a gel like state around this air pocket, in regions with amethyst formation, that gel contains a mix of silica and iron. Over time, this mineral gel pools in air pockets and it starts to crystalize. The crystals grow and grow until they seal the walls of the geode, stopping the process. The process of the silica crystalizing arranges the iron into a refracting structure, which gives amethyst its purple glow.
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