mineral

Pyrite Sun

Iron Sulfide (FeS2)

Hardness: 6-6.5 Mohs; Color: Brass-yellow to grayish-black (when oxidized); Luster: Metallic; Crystal Structure: Isometric; Form: Disc-like radial growth (concretion); Cleavage: Indistinct

Hardness: 6-6
Color: Brass-yellow to grayish-black (when oxidized)
Luster: Metallic

Identified July 6, 2026More mineral →

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Physical properties

Hardness: 6-6.5 Mohs; Color: Brass-yellow to grayish-black (when oxidized); Luster: Metallic; Crystal Structure: Isometric; Form: Disc-like radial growth (concretion); Cleavage: Indistinct

Formation & geological history

Formed in narrow seams of coal shale roughly 300 million years ago (Pennsylvanian period). The disc shape is caused by the mineral growing under extreme pressure between layers of shale, forcing it to expand laterally rather than in a cube.

Uses & applications

Primarily used as a collector's specimen and for metaphysical displays. Pyrite historically was used in the production of sulfuric acid.

Geological facts

Often called 'Pyrite Dollars' or 'Miner's Dollars,' these are almost exclusively found in coal mines near Sparta, Illinois. They are often mistaken for fossils like sand dollars or sunflowers due to their radial pattern.

Field identification & locations

Identify by the distinct radiating crystal structure from a central point and a metallic sheen. In the field, look within carbonaceous shale layers in coal mines. Keep them dry, as specimens from coal shale can be prone to 'pyrite disease' (oxidation).