Grain‐size Indices, Classification and Environment

SUMMARY Indices based on Wentworth phi values of Q 1 , Md and Q 3 are used for textural classification of sediments. Wentworth phi values enable a detailed subdivision. A nomenclature based on the Wentworth phi indices is developed. The indices, and to a smaller degree the names, show sorting and skewness based on integer phi units. The classification scheme gives a continuous scale from gravel to fine clay. The Q 1 MdQ 3 ‐indices can be used for distinction of river, marine and loess deposits. The addition of indices of the 1st and 99th percentile, giving 5‐digit indices, augments the possibilities for a determination of the environment: river deposits can be distinguished from beach and dune sediments and in more detail from shallow marine and coastal deposits. The indices can be handled by data‐processing machines.