081821c

Back to photographing tiny bits of a fossil microbial reef in NE Alabama. This is sort of an invisible-man puzzle. The white-over-light-gray area in the middle was once a fossil that later dissolved away. We know that because of all the little critters that grew on it (two white arrows on the left). The light-gray material labeled "S" is extremely fine lime sediment that partially filled the open space that formed when the mystery fossil dissolved. The white area, "C," is filled with calcite cement crystals. They precipitated from groundwater, and they formed last. Thin-section photomicrograph, 1 millimeter in long dimension. Mississippian age.