sedimentary

Conglomerate

Conglomerate (clastic sedimentary rock)

AI-generated identification · may be incorrect

Hardness: 6-7 Mohs (variable by clasts); Color: multicolored with grey, brown, red clasts in a fine-grained matrix; Luster: dull/earthy; Crystal structure: clastic (fragmental) texture with rounded grains over 2mm; Cleavage: none; Specific gravity: 2.6-2.8

Hardness: 6-7 Mohs (variable by clasts)
Luster: dull/earthy

Identified March 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in high-energy environments like riverbeds or alluvial fans where water current is strong enough to transport large clasts; lithified by compaction and cementation of rounded gravel. Found in geological formations ranging from Precambrian to Quaternary.

Uses & applications

Used primarily in the construction industry as aggregate for concrete and roadbeds; some high-quality specimens with colorful jasper or quartz clasts are cut and polished for lapidary use.

Geological facts

Conglomerate is often called 'pudding stone' in some regions, specifically the Hertfordshire Puddingstone in the UK; it indicates a past environment of flowing water, and similar formations were discovered on Mars by the Curiosity rover.

Field identification & locations

Identify in the field by looking for rounded pebbles or rocks embedded within a finer-grained matrix. It is commonly found near ancient river deltas, shorelines, or glacial deposits. Common in the Appalachian and Rocky Mountains.