mineral
Limonite-pseudomorph after Pyrite (Prophecy Stone)
Goethite and Limonite secondary minerals (FeO(OH)·nH2O) replacing Pyrite (FeS2)
Hardness: 5.0 to 5.5 Mohs scale. Color: Rusty brown, dark chocolate brown, to black. Luster: Dull, earthy, or sub-metallic. Crystal structure: Isometric (preserving the cubic or dodecahedral shape of the original pyrite). Cleavage: None. Specific gravity: 3.6 - 4.0.
- Hardness
- 5
- Color
- Rusty brown, dark chocolate brown, to black
- Luster
- Dull, earthy, or sub-metallic
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Physical properties
Hardness: 5.0 to 5.5 Mohs scale. Color: Rusty brown, dark chocolate brown, to black. Luster: Dull, earthy, or sub-metallic. Crystal structure: Isometric (preserving the cubic or dodecahedral shape of the original pyrite). Cleavage: None. Specific gravity: 3.6 - 4.0.
Formation & geological history
Formed through the process of 'pseudomorphism' where Pyrite crystals oxidation and hydration over millions of years result in the replacement of sulfur by iron oxides while maintaining the original crystal shape. Many are found in the White Desert of Egypt, dating from the Cretaceous to Eocene periods.
Uses & applications
Primarily used as metaphysical 'prophecy stones' in the spiritual community, geological display specimens, and as minor iron ores in some contexts.
Geological facts
These are often called 'pseudomorphs' (Greek for 'false form') because they have the chemical composition of one mineral but the crystal habit of another. The Egyptian specimens are famous for their unique, star-like or 'explosion' shapes.
Field identification & locations
Identify in the field by their distinct geometric/crystal shapes (cubes or 12-sided globes) combined with a rusty, metallic weight but no metallic luster. Common in weathered limestone or desert sedimentary environments.
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