sedimentary
Sandstone with Iron Concretion
Arenite with Limonite/Goethite Concretion
Hardness: 6-7 (quartz grains); Color: Red-brown, tan, or purple-hued; Luster: Dull or earthy; Structure: Clastic with a concentric mineral nodule; Cleavage: None
- Hardness
- 6-7 (quartz grains)
- Color
- Red-brown, tan, or purple-hued
- Luster
- Dull or earthy
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Physical properties
Hardness: 6-7 (quartz grains); Color: Red-brown, tan, or purple-hued; Luster: Dull or earthy; Structure: Clastic with a concentric mineral nodule; Cleavage: None
Formation & geological history
Formed through the accumulation of sand-sized mineral particles or rock fragments, followed by the precipitation of iron-rich minerals in pore spaces around a nucleus during diagenesis.
Uses & applications
Informational and decorative specimen; higher-quality concretions are collected for display. Large-scale sandstone is used in masonry and construction.
Geological facts
These circular structures are often mistaken for fossilized eggs or industrial parts, but they are purely geological results of chemical precipitation from groundwater.
Field identification & locations
Field identification involves looking for circular, harder-than-matrix nodules protruding from flat sandstone faces. Common in sedimentary basins worldwide.
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