Limonite after Pyrite (Prophecy Stone or Ironstone Concretion)

Physical Properties

Hardness: 4-5.5 (variable); Color: Dark brown to yellowish-brown; Luster: Dull to sub-metallic; Crystal structure: Pseudomorphic (retains the cubic or pyritohedron shape of the original mineral); Specific Gravity: 2.7-4.3.

Formation & Geological History

Formed via chemical weathering and oxidation where iron-rich minerals like pyrite are replaced by iron oxides (Limonite) while maintaining the original crystal shape. Often found in sedimentary or metamorphic host rocks.

Uses & Applications

Major ore of iron historically; currently highly valued by mineral collectors and the metaphysical community (often sold as 'Prophecy Stones').

Geological Facts

These are 'pseudomorphs', a Greek term meaning 'false form'. While the exterior shape is that of a cube or complex crystal, the internal chemistry has completely changed from iron sulfide to iron oxide.

Field Identification & Locations

Identify in the field by its distinct geometric shape contrasting with its earthy, rusty brown color and lack of metallic brassy luster associated with fresh pyrite. Commonly found in desert regions like the White Desert of Egypt.

Identified on: 4/25/2026

Mode: Standard