sedimentary

Conglomerate

Conglomerate (SiO2 matrix with various lithic clasts)

Hardness: 6.5-7 (variable based on clasts); Color: Tan, yellowish-brown, gray matrix; Luster: Dull or earthy; Crystal structure: Clastic/Fragmental; Cleavage: None; Contains rounded to sub-rounded pebbles.

Hardness: 6
Color: Tan, yellowish-brown, gray matrix
Luster: Dull or earthy

Identified June 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the lithification of rounded gravel and pebbles, typically in high-energy environments such as riverbeds, alluvial fans, or beaches where water movement rounds the stones before they are buried and cemented.

Uses & applications

Used primarily as coarse aggregate in the construction industry for concrete and road fill; occasionally used as a decorative stone in architecture or as a landscaping rock.

Geological facts

Conglomerate is often called 'puddingstone' by collectors because the rounded pebbles look like fruit in a pudding. It is the sedimentary equivalent of a 'time capsule' as it contains pieces of older rocks from various sources.

Field identification & locations

Identify in the field by looking for large, rounded rock fragments (clasts) larger than 2mm embedded within a finer-grained matrix. Commonly found in ancient river systems and sedimentary basins.

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Clastic Sedimentary Rock Grain (SiO2 dominated)

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