sedimentary

Conglomerate

Clastic sedimentary rock (Puddingstone)

Hardness: Variable (vines with clasts, usually 6.5-7 for quartz clasts); Color: Multicolored clasts in a tan, gray, or reddish matrix; Luster: Dull/Earthy matrix; Structure: Clastic with rounded grains >2mm; Specific Gravity: 2.6-2.8

Hardness: Variable (vines with clasts, usually 6
Color: Multicolored clasts in a tan, gray, or reddish matrix
Luster: Dull/Earthy matrix

Identified March 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the lithification of rounded gravel and boulders. High-energy environments like fast-moving rivers or beach waves provide the water action necessary to round the rock fragments before they are buried and cemented by minerals like calcite or quartz.

Uses & applications

Used in the construction industry as a coarse aggregate for concrete and road fill. Historically used for millstones and occasionally as a decorative building stone or 'puddingstone' jewelry pieces.

Geological facts

Conglomerate is often called 'puddingstone' because the rounded pebbles look like raisins or nuts in a pudding. It is the sedimentary 'cousin' of Breccia, which contains angular rather than rounded fragments.

Field identification & locations

Identify in the field by looking for 'rounded pebbles' embedded in a finer sandy matrix; it looks like natural concrete. Commonly found in ancient riverbeds, alluvial fans, and glacial deposits globally.

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