sedimentary

Conglomerate

Conglomerate (Detrital sedimentary rock)

Hardness: variable (depends on clasts and cement, usually 3-7 on Mohs scale); Color: Gray, brown, or buff matrix with multicolored rounded pebbles; Luster: Earthy to dull; Structure: Coarse-grained clastic with rounded clasts (>2mm); Specific Gravity: 2.6-2.8.

Luster: Earthy to dull

Identified March 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in high-energy environments such as river beds, alluvial fans, or beaches where water turbulence is strong enough to transport and round large stones. Over millions of years, these sediments are buried and lithified by mineral cements like calcite or silica.

Uses & applications

Used primarily in the construction industry as coarse aggregate for concrete and road fill. Occasionally used as ornamental stone if the clasts are colorful and well-indurated.

Geological facts

Conglomerates are often referred to as 'puddingstone' in certain regions of the UK and US due to their resemblance to a fruit pudding. Curiosity Rover discovered Martian conglomerate on Mars, proving that ancient fast-moving streams once existed there.

Field identification & locations

Identify by looking for rounded, water-worn pebbles embedded in a finer sandy or silty matrix. Found globally in ancient river basins and mountain fronts. Collectors look for 'Puddingstone' varieties with contrasting pebble colors.

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