sedimentary
Ferruginous Sandstone (Ironstone)
Sedimentary rock with high iron oxide content (Fe2O3 / FeO(OH))
Hardness: 5-6 (Mohs); Color: Dark brown to black with reddish-brown undertones; Luster: Dull to sub-metallic; Crystal Structure: Clastic/Amorphous; Cleavage: None; Density: High due to iron content.
- Hardness
- 5-6 (Mohs)
- Color
- Dark brown to black with reddish-brown undertones
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark brown to black with reddish-brown undertones; Luster: Dull to sub-metallic; Crystal Structure: Clastic/Amorphous; Cleavage: None; Density: High due to iron content.
Formation & geological history
Formed through the precipitation of iron oxides within sedimentary layers, typically in aqueous environments like lakes, bogs, or marine shelves. Often associated with the oxidation of iron-rich groundwater.
Uses & applications
Historically used as a low-grade iron ore. Today, it is primarily used in construction as road metal, decorative garden stones, and as a educational specimen for geology.
Geological facts
This rock can often be mistaken for a meteorite due to its dark, heavy, and pitted 'fusion crust' look (desert varnish), but it lack the internal metallic flecks and Widmanstätten patterns of space rocks.
Field identification & locations
Identify in the field by its high density (feels heavy for its size) and a reddish-brown streak when rubbed against unglazed porcelain. Commonly found in arid environments or areas with high iron-replacement in soil.
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