Ferruginous Breccia

Physical Properties

Hardness: 5-7 (clasts) vs 3-5 (matrix); Color: Reddish-brown, ochre, tan; Luster: Dull to earthy; Crystal Structure: Clastic; Cleavage: None; Specific Gravity: 2.8-3.5 depending on iron content.

Formation & Geological History

Formed through the mechanical breaking of pre-existing rocks into angular fragments (clasts), which are then cemented together by iron oxide-rich minerals precipitated from groundwater. This specimen appears to be from a terrestrial sedimentary environment.

Uses & Applications

Primarily used as a decorative stone, landscaping material, or for geological study. Occasionally used as a low-grade iron ore if the iron concentration is high enough.

Geological Facts

Breccia is distinguished from conglomerate by its angular clasts, which indicate that the fragments have not traveled far from their source before being cemented. The reddish 'rusty' color is caused by the oxidation of iron minerals, similar to the process of rusting metal.

Field Identification & Locations

Identify by looking for large, angular rock fragments held together by a different colored 'glue' or matrix. These are commonly found near fault zones or at the base of steep slopes where mechanical weathering is active. Check for magnetism, as some iron-rich matrices can be slightly magnetic.

Identified on: 4/25/2026

Mode: Standard