Concretion (Sandstone)

Physical Properties

Hardness: 6-7 (Mohs scale), Color: tan/brown/grey, Luster: dull/earthy, Structure: spherical/ellipsoid, Cleavage: none, Specific Gravity: 2.5-2.8

Formation & Geological History

Formed by the precipitation of mineral cement within the spaces between sediment grains, often around a nucleus like a leaf or shell. Commonly found in sedimentary rock layers like sandstone or shale.

Uses & Applications

Primarily used as decorative items, educational specimens, or garden ornaments; some types (like ironstone) can be an ore source.

Geological Facts

Commonly known as Moquie marbles or cannonballs when perfectly spherical. They can grow to several meters in diameter or be as small as a pebble.

Field Identification & Locations

Identify by its distinct spherical shape contrasting with the surrounding sedimentary bedding. Commonly found in eroding cliffs or streambeds.

Identified on: 5/1/2026

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