(rudites), coarse clastic rocks composed of fragments at least 1 mm in diameter. The fragments may be rounded (boulders, pebbles, gravel) or angular (blocks, chips). Psephites are divided into loose rocks (shingle, gravel) and cemented rocks (conglomerates, breccias). Psephites are usually formed in mountain regions, in river valleys, or in the coastal part of seas, where they frequently occur in thick beds. Some psephites, such as shingle, are used in construction.