mineral

Pyrite Sun (Pyrite Dollar)

Iron Disulfide (FeS2)

Hardness: 6-6.5 on Mohs scale; Color: Pale brass-yellow to grayish-white; Luster: Metallic; Crystal Structure: Isometric (radiating acicular crystals); Cleavage: Indistinct; Specific Gravity: 4.9-5.2.

Hardness: 6-6
Color: Pale brass-yellow to grayish-white
Luster: Metallic

Identified March 14, 2026More mineral →

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Physical properties

Formation & geological history

Formed roughly 300 million years ago during the Pennsylvanian Subperiod. They grew in narrow seams of coal and shale under extreme pressure, which forced the crystals to grow laterally in a flattened, radiating disk shape rather than cubes.

Uses & applications

Primarily used as display specimens for mineral collectors and occasionally used in unique jewelry pieces. Historically, pyrite was a source of sulfur and sulfuric acid.

Geological facts

These are unique to the coal mines of Illinois. Despite their appearance, they are not fossils of plants or sand dollars; they are purely mineralogical formations of iron sulfide.

Field identification & locations

Identify by its flattened disk shape with radiating striations from a central point and a metallic gold-like sheen. Primarily found in coal mines near Sparta, Illinois, often between layers of shale.