041721

 

Thin-walled snail shell containing micropelletal cement mixed with larger cylindrical fecal pellets. Coarse calcite cement filled the remainder of the shell. Shell embedded in microbial reef. Image area 2.5 millimeters high, Mississippian, North Alabama. Brown stain indicates the presence of iron minerals.

050219c

Limestone of the Knox Group, cross-section of a gastropod shell, mostly filled with lime mud (dark color like the surrounding matrix), remaining open space filled with calcite cement (clear and pink). Thin section, Kemper County Mississippi, approximately 3 miles below the surface.

A snail from the age of dinosaurs

Gyrodes, a steinkern. Imagine a snail, it dies and decays. The hotel fills with mud and the mud turns to stone. The shell dissolves away because it is made of the mineral aragonite, which dissolves pretty easily in water. What you have left is a steinkern.