Sandstone Concretion

Physical Properties

Hardness: 6-7 (Mohs scale), Color: Reddish-brown to tan, Luster: Dull/Earthy, Crystal Structure: Granular/Uncrystallized matrix, Cleavage: None, Specific Gravity: 2.0–2.6.

Formation & Geological History

Formed by the precipitation of mineral cement (often iron oxide or calcite) within the spaces between sediment grains. This process typically occurs early in the burial history of the sediment, before it is fully lithified into rock.

Uses & Applications

Primary use is for educational purposes, geological study, and decorative collecting. In some contexts, iron-rich concretions can be an indicator of iron ore deposits.

Geological Facts

Many people mistake these for fossils or meteorites due to their strange, lumpy shapes. They are often called 'Moqui Marbles' or 'Loess Puppies' depending on their specific mineralogy and location.

Field Identification & Locations

Identify by looking for a shape that is distinct from the surrounding rock layering, often appearing more rounded or lumpy. Commonly found in desert environments or eroding out of sandy cliffs.

Identified on: 4/13/2026

Mode: Standard