sedimentary
Sandstone with Ironstone Concretion
Arenite with Ferruginous Cement
Hardness: 6-7 (Mohs scale); Color: Tan, brown, and reddish-orange; Luster: Dull/Earthy; Structure: Clastic with a conchoidal-like fracture on the outer rind; Specific Gravity: 2.3-2.6
- Hardness
- 6-7 (Mohs scale)
- Color
- Tan, brown, and reddish-orange
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Tan, brown, and reddish-orange; Luster: Dull/Earthy; Structure: Clastic with a conchoidal-like fracture on the outer rind; Specific Gravity: 2.3-2.6
Formation & geological history
Formed by the accumulation of sand-sized mineral grains and rock fragments, subsequently cemented by silicate or iron minerals. The outer layer represents a ferruginous (iron-rich) weathering rind or concretionary shell formed by groundwater mineral deposition.
Uses & applications
Used extensively as a building material, paving stones, and for ornamental garden features. Finer sands from crushed sandstone are used in glass manufacturing.
Geological facts
Ironstone concretions can sometimes form around a fossil nucleus. The distinct 'shell' seen here is typical of 'spherical weathering' or 'rinded' rocks often found in riverbeds.
Field identification & locations
Identified by its gritty texture (feels like sandpaper) and visible layering. It is commonly found in sedimentary basins, riverbeds, and cliffsides globally; collectors look for well-defined color banding or concentric layers.
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