References 223

10 m

Figure 10.21. Scanning electron micrograph of Uruguay band.

The order of formation of the banding pattern is (1)→(4), and there can be cases that all four stages are present, or one part may be absent, or, in some cases, the cycle repeats.

From these observations of the texture, it is considered that agate precipitates from an aqueous solution containing SiO2, which intruded into a geode, and that in the aqueous solution clusters having right-handed and left-handed structures were already formed. When these clusters aggregate through electromigration due to the wall surface, the banding patterns discussed in (1) and (2) and large quartz crystals, (3), are formed. However, Uruguay banding is principally formed by gravitational settlement once the wall surface effect has diminished.

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