Laboratory abrasion tests on beach flint shingle

Laboratory tumbling experiments demonstrate that rounded flint beach shingle is less durable than commonlysupposed. The mean rate of abrasion for dark grey Sussex flints (Senonian) in the first few hours of tumbling increases withweight whereas that of white Normandy flints (Turonian and Coniacian) does not. Depending on pebble weight, the Sussex flintsabrade at up to six times the rate of the Normandy flints. Abrasion rates also vary according to tumbler load, the water:shingleratio, and tumbling period. The abrasion rate of Sussex flints decreases with time at a much greater rate than could be expectedfrom the reduction in size. The abrasion debris is mostly silt sized, but small quantities of sand are produced from samplescontaining larger pebbles. In situ abrasion of flint shingle is estimated to be significant, reducing the protection shingle beachesafford to cliffs thus exacerbating Chalk cliff instability.