sedimentary

Sandstone with Iron Concretion

Arenite with Limonite/Goethite Concretion

AI-generated identification · may be incorrect

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

Identified May 10, 2026More sedimentary →

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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.