sedimentary

Conglomerate

Conglomerate (clastic sedimentary rock)

Hardness: 6.5-7 (variable based on clasts); Color: Tan, brown, and grey; Luster: Dull to waxy; Crystal structure: Non-crystalline matrix with rounded clastic fragments; Cleavage: None; Specific Gravity: 2.6-2.8.

Hardness: 6
Color: Tan, brown, and grey
Luster: Dull to waxy

Identified July 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the lithification of rounded gravel and boulders. These are typically deposited in high-energy environments like fast-flowing rivers or beaches where water action rounds the stones before they are cemented together by minerals like calcite or quartz.

Uses & applications

Used in the construction industry as coarse aggregate for concrete and road beds. Well-cemented specimens are sometimes cut and polished for use as ornamental stone or stepping stones.

Geological facts

Conglomerate is often called 'puddingstone' because it looks like raisins or nuts in a pudding. Large formations can indicate the location of ancient riverbeds or alluvial fans.

Field identification & locations

Identify in the field by looking for large, rounded pebbles or cobbles (greater than 2mm) embedded in a finer-grained matrix. Commonly found in sedimentary basins and near old mountain ranges.

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