Monday's photo. The "cannonballs" are in reality concretions- places where, for one reason or another, cementing minerals were prompted to crystallize out in greater abundance than elsewhere. For example, often, in the center of a broken open concretion, one can find some kind of fossil. Fossils are often composed of calcite, and they could act as a nucleation surface upon which calcium and carbonate in solution in the pore spaces of the sediment would preferentially crystallize.
Concretions are quite common in sedimentary rocks, and are one of the things that the geologically innocent often mistake as fossils in and of themselves. As implied above, they may contain one or more fossils, or they may not. They are first and foremost artifacts of loose sediment becoming lithified.
Photo unmodified. March 8, 2012. FlashEarth location.
Is This Your Hat?
2 years ago