Article
Article
Conglomerate
Article By:
Siever, Raymond Formerly, Department of Geology, Harvard University, Cambridge, Massachusetts.
Last reviewed:March 2021
DOI:https://doi.org/10.1036/1097-8542.156600
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- Conglomerate, published November 2019:Download PDF
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The consolidated equivalent of gravel. Conglomerates are aggregates of more or less rounded particles greater than 2 mm in diameter. Frequently they are divided on the basis of size of particles into pebble (fine), cobble (medium), and boulder (coarse) conglomerates. The common admixture of sand-sized and gravel-sized particles in the same deposit leads to further subdivisions, into conglomerates (50% or more pebbles), sandy conglomerates (25–50% pebbles), and pebbly or conglomeratic sandstones (less than 25% pebbles). The pebbles of conglomerates are always somewhat rounded, giving evidence of abrasion during transportation; this distinguishes them from some tillites and from breccias, whose particles are sharp and angular (see illustration).
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