Soft rubber tumbling barrels were used to simulate natural abrasion of coral branches. Sealed barrels produced more sediment from coral branches than barrels with screen windows, and dead coral produced more sediment than live coral. Tumbled dead coral produced a gravel model (2-4 mm) of fragmented barnacles and a sand mode (0.2 mm) of coral. Tumbled live coral produced increasingly greater percentages of carbonate mud and increasingly finer sand grain-size modes. Tumbling barrels with screen windows yielded particles of unchanging size. Natural sediment with broken coral branches contained coral sand most abundantly between 0.125-0.250 mm, which is the same as produced by tumbling dead coral in barrels with screen windows. Strong grain-size modes at 0.2 mm produced by sonification and tumbling of live and dead coral in sealed and screen-window barrels support the Sorby principle of skeletal breakdown.--Modified journal abstract.