Conglomerate

Physical Properties

Hardness: variable (6.5-7 for quartz clasts); Color: mixed browns, tans, and grays; Luster: dull to earthy; Texture: clastic with rounded grains larger than 2mm; Composition: quartz, chert, and lithic fragments in a fine-grained matrix.

Formation & Geological History

Formed through the lithification of rounded river gravels or beach pebbles. The rounding of the stones indicates they were transported a long distance by high-energy water (rivers or waves) before being buried and cemented by minerals like calcite or silica.

Uses & Applications

Primarily used as a heavy coarse aggregate in construction and road building. Attractive specimens are used as 'pudding stones' for garden ornaments or lapidary work (jewelry and bookends) when the matrix is hard enough to polish.

Geological Facts

Known as 'pudding stone' in some regions because the rounded pebbles look like raisins or nuts in a pudding. It serves as a geological record of ancient high-energy water environments, such as fast-flowing mountain streams.

Field Identification & Locations

Identify in the field by looking for 'concrete-like' appearance with distinct, smooth, rounded pebbles (clasts) embedded in a finer sandy or silty matrix. Look for it in old riverbeds, alluvial fans, or shoreline deposits.

Identified on: 4/22/2026

Mode: Standard