The Secret Lives of Geodes

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Some time after this geode had formed, a metalic dendrite grew up through it and attached to the top plate.

Next, some kind of earth movement [earthquake, landslide, etc.] rotated the geode and slamed it hard to the right. A lot of material was disloged from the inside, and settled to the new bottom. The dendrite was also dislodged, leaving a stain in the silica jel around it, and settled slowly to the new "bottom." You can see the second attachment point on top of the rubble pile in the bottom middle.

Third, The ground containing the geode rotated back to the left. The dendrite detatched again and moved with it, taking some of the water layer with it. The silica now crystalyzed parallel to the "third bottom" as planes of agate and opal. The white planes are the opal. When the moisture dropped below a specific point [like the "dew point"] agate formed, above it, opal formed again.