mineral

Limonite Pseudomorph after Pyrite

Limonite (FeO(OH)·nH2O) replacing Pyrite (FeS2)

AI-generated identification · may be incorrect

Hardness: 4.0–5.5; Color: Dark brown to yellowish-brown or black; Luster: Dull, earthy, or sub-metallic; Crystal Structure: Isometric (retaining the cube shape of the original pyrite); Cleavage: None; Specific Gravity: 2.7–4.3

Hardness: 4
Color: Dark brown to yellowish-brown or black
Luster: Dull, earthy, or sub-metallic

Identified April 12, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the chemical weathering and oxidation of iron-rich sulfide minerals (pyrite). Over time, water and oxygen replace the sulfur in pyrite with hydroxide, creating a 'false form' (pseudomorph) where the mineral identity changes but the original crystal shape is preserved.

Uses & applications

Primarily collected as mineral specimens; historically used as a low-grade iron ore and as a source for yellow ochre pigment.

Geological facts

These are often called 'Prophecy Stones' in metaphysical circles or 'Devil's Dice' by collectors. Despite their change in chemistry, they maintain the perfect 90-degree angles of the original pyrite cubes.

Field identification & locations

Identify in the field by looking for perfect cubes or pyritohedrons that are brown and earthy rather than metallic gold. They are common in sedimentary localities like the White Desert in Egypt or the Llano Uplift in Texas.