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.
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Physical properties
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.
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.
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