Conglomerate is a siliciclastic sedimentary rock consisting of a mix of large & small grains (it is poorly sorted).  The larger grains (pebbles or cobbles or boulders) in conglomerates are rounded to subrounded in shape.  The finer-grained matrix is usually sand or mud.


Shown below is a quartzose conglomerate, having rounded quartz pebbles and quartz sand.  Some conglomerates are feldspathic - they have an abundance of K-feldpar pebbles.  Some conglomerates are lithic - they have an abundance of large clasts composed of a variety of other rock types.


Most conglomerates were deposited in alluvial fan environments, in many stream/river environments, and in some very shallow marine environments.



Conglomerate (quartzose conglomerate)



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