sedimentary

Conglomerate

Conglomerate (clastic sedimentary rock)

Composed of rounded gravel-sized clasts (>2mm) held together by a matrix of sand/silt and mineral cement; Hardness: variable (3-7 Mohs) based on clasts; Color: multi-colored/mottled; Luster: earthy/dull; Structure: clastic/fragmental.

Hardness: variable (3-7 Mohs) based on clasts
Color: multi-colored/mottled
Luster: earthy/dull

Identified March 27, 2026More sedimentary →

Identify your own rocks.

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

App Store Google Play

Physical properties

Formation & geological history

Formed in high-energy environments like riverbeds, alluvial fans, or beaches where water current is strong enough to transport and round large stones. Over millions of years, these deposits are buried and lithified through pressure and mineral precipitation.

Uses & applications

Used primarily in the construction industry as coarse aggregate for concrete and roadbeds; sometimes used as architectural stone or for interior decoration if it contains high-contrast colorful clasts.

Geological facts

Conglomerates are often referred to as 'puddingstone' because they resemble a fruit pudding; they indicate a specific paleoenvironment where ancient high-velocity water once flowed, helping geologists map ancient river systems.

Field identification & locations

Identify in the field by looking for 'stones within a stone'—specifically rounded pebbles or cobbles embedded in a finer-grained matrix. Found globally in ancient sedimentary basins, river valleys, and mountain foothills.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone (Quartz-rich)

Arenite (SiO2)

sedimentary

Sandstone (with man-made markings)

Arenite (composed primarily of Quartz, SiO2)

sedimentary