igneous
Polymict breccia (likely impact breccia)
Polymict lithic breccia; composition appears basaltic/mafic clasts in a dark, fine-grained matrix
AI-generated identification · may be incorrectAngular to subangular gray, tan, and dark clasts cemented in a black matrix; generally Mohs ~5–6, dull to slightly vitreous luster, no consistent cleavage, and variable density around 2.7–3.1 g/cm³.
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Physical properties
Angular to subangular gray, tan, and dark clasts cemented in a black matrix; generally Mohs ~5–6, dull to slightly vitreous luster, no consistent cleavage, and variable density around 2.7–3.1 g/cm³.
Formation & geological history
Formed when pre-existing rocks were violently fractured and fragmented, then compacted and cemented; the texture is consistent with impact ejecta, though volcanic or tectonic breccia is also possible. Exact age and origin require locality or laboratory analysis.
Uses & applications
Primarily a geological specimen or educational sample; rarely used decoratively or as aggregate because of its heterogeneous, fractured texture.
Geological facts
The angular clasts distinguish breccia from conglomerate, whose clasts are rounded. A meteorite-impact origin may be supported by shock features, melt glass, or elevated nickel/chromium, but cannot be confirmed visually.
Field identification & locations
Look for sharp-edged fragments, contrasting lithologies, and a cementing matrix; common examples occur near volcanic centers, fault zones, and impact craters. A thin section or geochemical test can establish provenance.
