mineral

Limonite pseudomorph after Pyrite

Goethite/Limonite FeO(OH)·nH2O

Hardness: 4-5.5; Color: Yellowish-brown to dark brown; Luster: Dull or earthy; Crystal structure: Isometric (original cubic form preserved); Cleavage: None; Specific Gravity: 2.7-4.3

Hardness: 4-5
Color: Yellowish-brown to dark brown
Luster: Dull or earthy

Identified June 26, 2026More mineral →

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Physical properties

Hardness: 4-5.5; Color: Yellowish-brown to dark brown; Luster: Dull or earthy; Crystal structure: Isometric (original cubic form preserved); Cleavage: None; Specific Gravity: 2.7-4.3

Formation & geological history

Formed through the chemical weathering and oxidation of original pyrite crystals in sedimentary or metamorphic environments. The original iron sulfide is replaced by iron oxides while maintaining the cube shape.

Uses & applications

Primarily a collector's specimen; historically used as a source of iron ore (pigment) or 'ochre' in various industries.

Geological facts

These are often called 'Devil's Dice' by collectors because of their natural cubic shape. They are 'pseudomorphs,' a term meaning 'false form' because the mineral is brown limonite but the shape is that of the original pyrite.

Field identification & locations

Identify by the distinct cubic or 'dice' shape combined with a dull, rusty brown color. Found in weathered outcrops of shale, phyllite, or schist, often in the Piedmont region of the US or across Europe.

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