USGS CMG InfoBank: Sizes of Clastic Sediment

Source: Annenberg/CPB Resources - Earth Revealed - 17. Sedimentary Rocks: The Key to Past Environments

Keywords: "sedimentary rock", "clastic sediment", erosion, boulder, cobble, pebble, sand, silt, clay, "grain size"

Our transcription: One of the most common forms of sediment is referred to as "clastic" from the Greek word for "broken."

Fragments of rocks and minerals falling from an eroded outcrop are examples of clastic sediment.

Clastic sediments are classified by size ranging from large "boulders", through smaller "cobbles" and "pebbles", then grains of "sand", even smaller grains of "silt", and, finally, down to the finest sediment of all, "clay", which has the consistency of flour.