mineral

Limonite with Opal infusion

FeO(OH)·nH2O (Limonite) / SiO2·nH2O (Opal)

Hardness: 4-5.5 (Limonite), 5.5-6.5 (Opal); Color: Earthy brown to reddish-orange with iridescent blue/purple patches; Luster: Dull to sub-vitreous; Structure: Amorphous to microcrystalline; Specific Gravity: 2.7-4.3

Hardness: 4-5
Luster: Dull to sub-vitreous

Identified March 5, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the secondary weathering of iron-rich minerals (limonite) and the precipitation of silica-rich fluids in cracks and voids producing precious or common opal. Found in oxidization zones of iron ore deposits.

Uses & applications

Primary source of iron ore (limonite) and as a semi-precious gemstone or specimen for mineral collectors when containing opal.

Geological facts

This specimen appears to be 'Boulder Opal' or ironstone with opal, where the opal forms in the iron-rich cracks of the host rock. Limonite is not a single mineral but a mixture of hydrated iron oxide minerals.

Field identification & locations

Identify by the heavy, rusty-colored gossan matrix containing glassy or colorful silica seams. Found in arid regions like Queensland, Australia, or iron-rich hydrothermal sites.

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