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Scanning electron microscope techniques show that Eocene opaline claystones (fuller's earth and buhrstone) of the Atlantic and Gulf Coastal Plain, deposits long considered volcanic in origin, are actually highly altered diatomites formed as transgressive facies in normal marine continental shelf environmnents. These findings are in agreement with a biogenic origin for time-equivalent horizon A and A deep-sea cherts of the North Atlantic and Caribbean.

The microarchitecture of gastropod nacre reveals deposition of aragonite in the form of crystal stacks and differs markedly from the characteristic microstructure of pelecypod nacre. The structure permits direct observation of both organic and mineral phases of deposition on a growth surface topography that is ideal for the study of processes of mollusk shell calcification. The stack mode of deposition is functionally useful to the animal because it increases the number of crystals which can form and develop on the growth surface at one time.

Scanning electron microscopic studies have revealed the configurations of the growth surfaces of scleractinian coral exoskeletons. Skeletal surfaces exhibit profuse growths of minute elongate aragonite crystals which, on basal and mural surfaces, are punctuated by scars. It is suggested that these scars are sites of attachment for the specialized processes that connect the living tissues of polyps to the nonliving skeleton. Patterns formed by the attachment scars are taxonomically significant.