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.