Chert Formation
Unknown excavation source
Measurements: 6" x 4"; weight not given

A concretion of limestone and possibly flint. In a process known as diagenesis, chert, including flint, forms within limestone when silica-rich fluids replace calcium carbonate with microcrystalline quartz. Chert most often appears as nodules, but can also form continuous layers, called bedded chert.

The silica needed to form chert primarily comes from the skeletal remains of silica-secreting marine organisms like diatoms and radiolarians. When these microscopic organisms die, their skeletons sink and accumulate on the seafloor as a silica-rich sediment. Over time, this silica-rich water undergoes a chemical replacement process forming into a solid sedimentary rock.

Chert and flint are prized for creating arrowheads, blades, and other tools, a process known as flintknapping. Some chert varieties have unusual or beautiful colors, patterns, and translucence, making them sought-after for collectors and lapidary work.

For ordinary chert nodules found in fields or creek beds, an auction would likely attract very little interest. However, for a specialty auction featuring mineral specimens, geological materials, or high-end flintknapping stock, a premium nodule could attract attention from the right bidders.