Corals:
Corals are colonial and so their framework may encompass many individual animals.The overall shape varies tremendously across different species, but in general, unless broken into very small bits (just pieces of the walls) coral fragments will contain ample internal porosity. Coral mineralogy varies with taxonomy. The two main groups of now extinct Paleozoic corals, the rugosans and the tabulates, secreted calcitic skeletal frameworks in which the calcite fibers are somewhat smaller and less apparent than in the brachiopods and bryozoans. The most abundant calcified corals of the post-Paleozoic, the scleractinians, secrete shells of aragonite.