Illinois Pyrite Suns: Nature’s Metallic Masterpieces

Illinois pyrite suns, also called “miner’s dollars” or “pyrite dollars,” are striking, disk-shaped mineral formations composed of iron sulfide (FeS₂), better known as pyrite. Found almost exclusively in the coal mines of southern Illinois, particularly near Sparta in Randolph County, these unusual specimens are admired for their radiant, sun-like patterns and metallic luster. Unlike typical pyrite crystals, which often grow in cubic or irregular forms, pyrite suns are remarkably flat, typically ranging from 1 to 6 inches in diameter, though larger examples exist.

These natural formations originated roughly 300–350 million years ago during the Pennsylvanian period, a time when much of present-day Illinois was covered by coastal swamps, dense vegetation, and shallow seas. Pyrite suns formed within the Anna Shale, a gray, carbon-rich rock layer that sits above the Herrin Coal Seam. As layers of sediment accumulated and compacted, chemical reactions involving sulfur and iron under low-oxygen conditions led to the growth of pyrite. Because they formed between tightly compacted layers of shale, these crystals were forced to grow outward rather than upward, resulting in their unique, flattened, radiating structures.

Pyrite suns were first discovered by coal miners in the 19th century. Workers often found them embedded in the shale above coal seams and would collect them out of curiosity. Some thought they were fossilized plants or sea creatures; others considered them lucky or symbolic, giving rise to their nickname “miner’s dollars.”

Today, Illinois pyrite suns are considered rare and collectible. With many of the region’s coal mines closed, new specimens are harder to come by. Well-preserved suns are sought after by mineral collectors, museums, and geology enthusiasts. However, pyrite is sensitive to humidity and air exposure; over time, it can oxidize and deteriorate, turning into powdery iron sulfate if not properly stored.

Their beauty, rarity, and geological significance make Illinois pyrite suns a fascinating window into the Earth’s deep past—where pressure, chemistry, and time combined to create something that looks like it was made by design. Whether viewed as scientific curiosities or natural works of art, pyrite suns remain one of the Midwest’s most intriguing mineralogical treasures.

7 Fun facts about Pyrite Suns:

1. Unique Disk Shape
Pyrite suns are known for their flat, round form and radiating crystal patterns that resemble a stylized sunburst.

2. Found Only in Illinois
These striking formations are almost exclusively located in the Illinois Coal Basin, especially near Sparta and Randolph County.

3. Ancient Origins
They formed around 350 million years ago during the Pennsylvanian period, when the region was covered by coastal swamps and shallow seas.

4. Grown in Tight Spaces
Pyrite suns grew between thin layers of shale, which restricted vertical growth and led to their unusual, flattened shape.

5. Discovered by Coal Miners
Miners in the 1800s often found these while working the coal seams and collected them as natural oddities.

6. Mistaken for Fossils
Their unique appearance has led people to confuse them with fossilized lily pads, sand dollars, or even ancient coins.

7. Prone to Deterioration
When exposed to air and moisture, pyrite can oxidize and break down over time, sometimes giving off a sulfur smell.

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