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Posted by: Daniel Bennett
picture if you will oil and water shook up with little balls of oil swirling in water. but instead liquid quartz balls swirling in liquid magma. like a red hot stone dropped in cold water liquid magma trembles and shakes as it surfaces to atmospheric temp. the bands in agates form when vibrations from rapidly cooling basalt cause "ripples" in the solidifying quartz balls. like moving water vibrating quartz takes longer to" freeze" so it freezes up layer by layer starting from the outside. in the case of so called "water level agates" when the magma first surfaces vibrations are coming from all direction and a little later the majority of vibrations start coming from below. by that time the outermost part of the agate is solidifying but the center is still fluid and so the perimeter bands turn in to flat parallel bands. which also points towards water level agates coming from the uppermost parts of the flow. agate "eyes" spherolites are from a higher temp melting point particle present in the quartz during the vibrations often finding its way to the outside edge while any gas bubble present will tend to gravitate to the center...