sedimentary

Conglomerate

Conglomerate (clastic sedimentary rock)

Hardness varies based on clast composition (typically 6.5-7 for quartz clasts); color is often dark grey to black matrix with multicolored rounded clasts; luster is dull to earthy for the matrix; texture consists of rounded granules and pebbles exceeding 2mm in diameter embedded in a finer sandy or silty matrix.

Identified March 18, 2026More sedimentary →

Explore Conglomerate in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through the lithification of rounded river or beach gravel. The rounded shape of the pebbles indicates they were transported long distances by high-energy water (rivers or waves) which eroded sharp edges before being buried and cemented over millions of years.

Uses & applications

Primarily used as a heavy construction material, coarse aggregate for concrete, and as a decorative building stone. It can also be a reservoir rock for petroleum and natural gas exploration.

Geological facts

Conglomerate is often called 'puddingstone' because it resembles a fruit pudding. On Mars, NASA's Curiosity rover found conglomerate outcrops, providing concrete evidence that ancient Mars once had vigorous flowing streams.

Field identification & locations

Identify in the field by looking for rounded pebbles (clasts) that are 'glued' together by a finer-grained matrix. Unlike Breccia, which has sharp/angular fragments, Conglomerate always features smooth, rounded stones. Common in ancient riverbeds and alluvial fans.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary