Conglomerate

Physical Properties

Hardness: variable depending on clast composition (typically 6-7 if quartz-based); Color: grey, brown, rusty; Luster: dull/earthy matrix with various clast lusters; Structure: clastic texture with rounded pebbles (>2mm) in a fine-grained matrix; Cleavage: none.

Formation & Geological History

Formed through the lithification of rounded gravel and boulders, typically in high-energy environments such as riverbeds, alluvial fans, or mountain-front streams where water moves fast enough to roll large rocks.

Uses & Applications

Used primarily in the construction industry as aggregate for concrete and road stone. Occasionally used as a decorative building stone or for landscaping.

Geological Facts

Conglomerate is often called 'puddingstone' because the rounded pebbles look like raisins or nuts in a pudding. They are significant indicators of ancient river systems and shorelines in the geological record.

Field Identification & Locations

Identify in the field by looking for rounded, water-worn pebbles or 'clasts' embedded within a finer sandy or silty matrix. It is found worldwide in sedimentary basins and near former or current mountain ranges.

Identified on: 4/15/2026

Mode: Standard