sedimentary

Breccia

Clastic Breccia

Hardness (clasts) usually 6-7 if silica-based; colors include mottled grays, tans, and blacks; dull luster; clastic texture with large angular fragments; poor cleavage overall; specific gravity varies by matrix composition (2.4-2.8).

Identified June 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of large, angular rock fragments usually resulting from landslides, fault zones, or debris flows. The fragments are later cemented together by minerals like calcite or silica before they can be rounded by water transport.

Uses & applications

Primarily used as a decorative building stone for countertops and walls, an aggregate in the construction of road bases, and as a popular specimen for educational geology kits.

Geological facts

The key difference between breccia and conglomerate is the shape of the fragments; breccia's angular pieces prove the rock pieces were not transported far from their source, as they didn't have time to be eroded into smooth circles.

Field identification & locations

Identified by the distinct 'broken' look of its internal rocks. Found in fault zones (fault breccia), at the base of steep slopes (talus), or near impact craters. Collectors should look for sharp-edged clasts and a matrix that matches local geology.