sedimentary
Ironstone (Limonite/Goethite Concretion)
Ferruginous Sedimentary Rock (composed of Goethite FeO(OH) and Limonite)
Hardness: 4.0 - 5.5; Color: Dark brown to black with yellow-ochre oxidation; Luster: Dull or sub-metallic; Structure: Amorphous or microcrystalline; Highly dense and often heavy for its size.
- Hardness
- 4
- Color
- Dark brown to black with yellow-ochre oxidation
- Luster
- Dull or sub-metallic
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Physical properties
Hardness: 4.0 - 5.5; Color: Dark brown to black with yellow-ochre oxidation; Luster: Dull or sub-metallic; Structure: Amorphous or microcrystalline; Highly dense and often heavy for its size.
Formation & geological history
Formed via the precipitation of iron oxides in sedimentary environments, often as bog iron or within sandstone beds. The dark coating is often a desert varnish or manganese/iron oxide crust developed over long-term exposure.
Uses & applications
Historically used as a low-grade iron ore; commonly used today as decorative garden stones or for geological study. Higher quality specimens may be used for earthy pigments.
Geological facts
These rocks are often mistaken for meteorites due to their heavy weight and dark, weathered exterior (fusion crust mimicry), but they lack the internal metal grains and Widmanstätten patterns of true meteorites.
Field identification & locations
Identify in the field by its high density and characteristic rusty-yellow streak when scratched against unglazed porcelain. Commonly found in riverbeds, desert pavements, and iron-rich soil deposits.
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