sedimentary

Conglomerate

Clastic sedimentary rock (Conglomerate)

Hardness: 6.5-7 (typically mirrors the hardness of the quartz matrix), Color: Reddish-brown with embedded dark grey and tan clasts, Luster: Dull/Earthy, Crystal Structure: Clastic (non-crystalline), Cleavage: None (fractures around clasts), Specific Gravity: 2.6-2.8

Hardness: 6

Identified March 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in high-energy environments like riverbeds, alluvial fans, or beaches where water currents are strong enough to transport large, rounded pebbles. Over time, these pebbles are buried and cemented by minerals like calcite or silica. This specimen likely dates from the Phanerozoic eon.

Uses & applications

Commonially used as a coarse aggregate in the construction industry for concrete and road beds. Higher-quality, colorful specimens are sometimes cut as 'puddingstone' for ornamental use or lapidary work.

Geological facts

Conglomerate is often called 'nature's concrete.' On Mars, NASA's Curiosity rover discovered conglomerate outcrops, providing key evidence that vigorous ancient streams once flowed across the Martian surface.

Field identification & locations

Identify by looking for rounded pebbles (clasts) larger than 2mm firmly embedded in a finer-grained matrix. Unlike Breccia, which has angular fragments, Conglomerate fragments are rounded by water erosion. Common in sedimentary basins worldwide.

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