sedimentary

Sandstone Concretion

Clastic Sedimentary Concretion (SiO2 with Iron Oxide)

AI-generated identification · may be incorrect

Hardness: 6-7 (Mohs); Color: Tan, brown, ochre; Luster: Dull/Earthy; Crystal structure: Amorphous/Granular clastic; Cleavage: None; Specific gravity: 2.3-2.6

Hardness: 6-7 (Mohs)
Color: Tan, brown, ochre
Luster: Dull/Earthy

Identified June 13, 2026More sedimentary →

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Physical properties

Hardness: 6-7 (Mohs); Color: Tan, brown, ochre; Luster: Dull/Earthy; Crystal structure: Amorphous/Granular clastic; Cleavage: None; Specific gravity: 2.3-2.6

Formation & geological history

Formed by the precipitation of mineral cement (often calcite or iron oxide) within the spaces between sediment grains, usually around a nucleus like a shell or leaf. They form in sedimentary basins over millions of years.

Uses & applications

Used primarily as decorative garden stones, oddities for collectors, and occasionally used in landscaping. Historically, some were used as primitive tools or pigments.

Geological facts

Concretions are often mistaken for fossils, eggs, or man-made artifacts because of their symmetrical or unusual shapes. The Moqui Marbles are a famous type of sandstone concretion found in Utah.

Field identification & locations

Identified by its rounded or bulbous shape that differs from the surrounding rock layers. Often found in eroded sandstone cliffs or riverbeds. Look for concentric layering or 'capping' on the outer shell.