sedimentary
Ferruginous Sandstone (Ironstone)
Sedimentary rock with Limonite/Goethite cement
Hardness: 5-6 (variable); Color: Dark brown, reddish-orange, or black; Luster: Dull to earthy; Crystal structure: Clastic (sand grains); Cleavage: None; Specific gravity: 3.0-4.0 (denser than regular sandstone due to iron content).
- Hardness
- 5-6 (variable)
- Color
- Dark brown, reddish-orange, or black
- Luster
- Dull to earthy
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Physical properties
Hardness: 5-6 (variable); Color: Dark brown, reddish-orange, or black; Luster: Dull to earthy; Crystal structure: Clastic (sand grains); Cleavage: None; Specific gravity: 3.0-4.0 (denser than regular sandstone due to iron content).
Formation & geological history
Formed through the accumulation of sand grains subsequently cemented by iron oxides (like hematite or limonite) precipitated from groundwater. Often found in Phanerozoic sedimentary basins.
Uses & applications
Historically used as a low-grade iron ore; commonly used today as building stone, decorative landscaping, and road base material.
Geological facts
Ironstone nodules like this one often form around organic nuclei like leaves or shells. In many regions, they are known for containing excellently preserved fossils because the iron shell protects the interior.
Field identification & locations
Identify by its distinct rusty-brown streak when scratched against porcelain and its relatively high weight for its size. Look for it in weathered cliffs or as rounded 'nodules' in riverbeds.
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