Pyrite

specimen number:
9892192

location:
Sparta, Randolph Co., Illinois, USA

description:
What is called a pyrite sun, a perfectly shaped disc of sparkling golden crystallized pyrite. Complete all around and in excellent condition.

The coal-mining region near Sparta in Randolph County, Illinois, sits within the vast Illinois Basin, where Pennsylvanian-age organic matter, clay, and iron-sulfide-rich sediments accumulated over 300 million years ago. Underground coal miners working deep subterranean seams, particularly in the Carbondale Formation, regularly recovered disk-shaped mineral formations known as pyrite suns, pyrite dollars, or miner dollars from narrow bedding planes in the overlying black shale beds. Although historically mistaken for fossilized plant life or sand dollars due to their rounded, flat shapes, pyrite suns are actually inorganic diagenetic concretions. They formed when sulfur-rich fluids and iron precipitated under intense pressure within tightly compacted shale layers, forcing the growing iron sulfide crystals to radiate outward laterally along horizontal planes rather than expanding into standard three-dimensional cubes. Commercial coal mine closures in the Sparta area have made fresh discoveries extremely rare, elevating these distinct, golden, starburst-patterned disks into prized historic collector items.

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