sedimentary

Conglomerate

Conglomerate (clastic sedimentary rock)

Hardness: variable depending on clasts (usually 3-7 Mohs); Color: tan, brown, or grey matrix with multi-colored rounded pebbles; Luster: dull/earthy; Structure: clastic texture with large rounded fragments (>2mm) embedded in a fine-grained matrix.

Hardness: variable depending on clasts (usually 3-7 Mohs)
Luster: dull/earthy

Identified March 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in high-energy environments like fast-flowing rivers or beaches where rounded stones are deposited and later lithified. Usually associated with alluvial fans or glacial outwash plains. Ages range from Precambrian to Cenozoic.

Uses & applications

Used primarily as low-grade construction aggregate, fill material, or decorative landscape stone. Very rarely used for architectural dimension stone due to variable structural integrity.

Geological facts

Conglomerate is often called 'puddingstone' in localized areas, especially in the UK and Northern USA. It serves as an indicator of ancient river systems and shorelines, helping geologists map historical water flow.

Field identification & locations

Identify by looking for rounded, water-worn pebbles (clasts) that are cemented together. Unlike Breccia, which has sharp angled fragments, conglomerate has smooth, rounded stones. Common in ancient riverbeds or mountain foothills.

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