mineral

Limonite Pseudomorph after Pyrite

Limonite (Hydrous iron oxides, FeO(OH)·nH2O) replacing Pyrite (FeS2)

AI-generated identification · may be incorrect

Hardness: 4-5.5 (Mohs scale), Color: Dark brown to yellowish brown, Luster: Dull or earthy, Crystal structure: Isometric (preserving the cubic shape of the original pyrite), Cleavage: None, Specific gravity: 2.7–4.3

Hardness: 4-5

Identified April 2, 2026More mineral →

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Physical properties

Formation & geological history

Formed through oxidation and hydration where water and oxygen chemically transform original pyrite crystals into a mixture of iron oxides (limonite) while preserving the external geometric shape. This is called a pseudomorph (false form).

Uses & applications

Primarily a collector's specimen. Limonite is historically an iron ore and is also used as an earthy pigment (yellow ochre).

Geological facts

Commonly known as 'Prophecy Stones' in metaphysical circles (specifically those from Egypt), these specimens are fascinating because they look like one mineral but are chemically another. They are essentially 'geological ghosts'.

Field identification & locations

Identify in the field by looking for distinct cubic or pyritohedron shapes that are dark brown and non-metallic, unlike true pyrite. They are commonly found in arid desert environments like the White Desert of Egypt or in weathered sedimentary iron-rich beds.