Geode Formation

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Geodes are formed in highly silicious melt flows that are just above the melting point of silica where "frazzle [silica w, lussatite, needle chrystobalite depending on the Authority quoted] " forms. Glide planes bring the needles together allowing them to form spheres around high valence impurities [often red] in the melt. The sphere grows into several glide planes and then grows even more quickly as in Stage A. Stage B is a Consolidation step as needles "jump" from smaller spheres to larger spheres, and the small spheres are burried in the larger mass of radiating needles. Stage C is a Transition step as the melt cools and stiffens. The needles in the sphere cool below the temperature that allows them to maintain a needle structure, and recrystalize in a much denser form, often leaving a casting in the material left between the needles that sticks to the now hardening melt surrounding the sphere and becomes the geode outer shell. Stage D, A vacuum now exists in the center of the sphere that can suck in ground waters and desolved silica, calcite, etc. from the surrounding area. Often the geodes at the top of a geode bed are "duds, " that is, they sucked in air or water and are now hollow. The next layer down are often half filled, and have a lot of white opal planes in them. The next layer down is often "fortification agate" that crystalized from all exterior plates to the center, as heat radiated out equally in all directions. The final layer is often formed with layered agate that cooled and crystalized from the bottom up as heat radiated out faster that way. E is a drawing of a "geode within a geode" that is sometimes found. The fractures allowed seperation at a large enough spherical diameter to allow the inner part to also shrink and fill with agate.