CompuServe Messages

Kamron: I'm probably late with this reply but thought it might be helpful. I can't remember the exact process of geode formation but my old "Sedimentary Rocks" text says that geodes grow by expansion from cavities in fossils filled with a common salt solution and isolated by a layer of gelatinous silica. In the course of time, waters outside the cell freshen, and osmosis builds up internal pressure, forcing fluids (and precipitation or solidification of the gel) against the cell walls. Expansion continues until the cell volume reaches equilibrium with the surrounding fluids. This is followed by shrinkage and cracking, allowing circulating groundwaters to deposit calcite, quartz, etc. in horizontal layers. Frank Ludeman