mineral

Limonite Pseudomorph after Pyrite

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

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 →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

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.

Other mineral specimens

See all

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Green Apatite on Albite

Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]

mineral

Epidote

Epidote - Ca2(Al2,Fe3+)3(SiO4)3(OH)

mineral