igneous
Breccia
Polymictic volcanic breccia (likely basaltic-andesitic matrix)
AI-generated identification · may be incorrectDark, fine-grained to glassy matrix containing abundant angular to subangular fragments of pale gray, tan, and reddish rock; typically hardness 5–7, dull to slightly vitreous luster, no consistent cleavage, and specific gravity about 2.5–3.0.
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Physical properties
Dark, fine-grained to glassy matrix containing abundant angular to subangular fragments of pale gray, tan, and reddish rock; typically hardness 5–7, dull to slightly vitreous luster, no consistent cleavage, and specific gravity about 2.5–3.0.
Formation & geological history
Formed when volcanic or tectonic rock fragments accumulate and become cemented, commonly during explosive eruptions or faulting; its exact geological age cannot be determined from the image and depends on locality.
Uses & applications
Used locally as crushed aggregate, dimension stone, and ornamental material; attractive polished pieces are collected but are generally not gemstone-grade.
Geological facts
The angular clasts distinguish breccia from conglomerate, whose clasts are rounded. The varied fragments indicate a polymictic origin and may record multiple source rocks or eruptive events.
Field identification & locations
Identify it by its dark cementing matrix and sharp-edged, compositionally varied clasts; a hand lens, fresh fracture, and locality information help distinguish volcanic breccia from impact or fault breccia. Common in volcanic terrains, fault zones, and impact structures.
