Pyrite Suns, also called Miner’s Dollars, are disk-shaped concretions of pyrite crystals formed under immense pressure, and found in Pennsylvanian-age rocks, (approximately 300 million years old), 200 to 250 feet below ground in the coal mines around Randolph County, Sparta, Illinois. The disks are found a few inches above the coal seam in thin, pyrite-rich shale layers.
The flattened, radiating form of pyrite suns is the result of pressure from overlying sediments. Rather than growing upward into typical cubic or nodular shapes, the pyrite crystals were forced to expand laterally (or radially) between compacted layers of shale, forming thin, circular patterns.
This pyrite sun measures roughly 4” x 3.5” (10.3 cm x 9.3 cm).
