Final answer:
The grain shape of conglomerate rock is typically rounded and the rock is coarse-grained, indicating significant transport by water from their source, leading to abrasion and similarly sized, well-sorted grains.
Step-by-step explanation:
The grain shape of a rock like conglomerate can provide important clues about the rock's history. Conglomerates are composed of distinct, large, rounded pebbles, cobbles, and boulders cemented together. This type of sedimentary rock is considered coarse-grained, with the grain size of the individual clasts commonly being greater than 1 millimeter. Conglomerate rocks often form in environments where there is a significant amount of water energy, such as swift rivers, which can carry and round the larger clasts before they are deposited and eventually cemented into rock.
The roundness of the grains within a conglomerate indicates that the clasts have been transported over some distance from their source, which causes them to become more rounded due to abrasion and weathering. Conglomerates with well-rounded and similarly sized grains are described as well-sorted, pointing to a constant and vigorous transport mechanism, which typically involves water.