The hard outer structure of the stony corals that resembles a tree branch or a glob is an exoskeleton that accretes as a result of the calcium carbonate the coral secretes over a prolonged period of time.
石珊瑚外形呈樹枝或團塊的堅硬部分，是珊瑚在多年生長後，分泌出碳酸鈣堆積形成的「骨骼」。