Conglomerate, Sandstone, Siltstone: Particle Size Comparison in Sedimentary Rocks

Which of the following lists is written in order of decreasing particle size?

a. sandstone, siltstone, conglomerate

b. sandstone, conglomerate, siltstone

c. conglomerate, sandstone, siltstone

d. siltstone, sandstone, conglomerate

Answer

The correct decreasing order of the particle size is: Conglomerate, Sandstone, Siltstone.

Conglomerates are rocks with particle sizes ranging from the size of a pebble (2 mm) to the size of a boulder (256 mm). They are made up of large, rounded fragments cemented together. Sandstones have particle sizes varying from 1/16 mm to 2 mm, consisting mainly of sand-sized grains. Siltstones, or silt rocks, have particle sizes ranging from 1/256 mm to 1/16 mm, with fine-grained texture.

Therefore, in the given list, conglomerate has the largest particle size, sandstone has a medium particle size, and siltstone has the smallest particle size.