The chemical composition of the diatom frustule

Summary

This paper describes the X-ray diffraction studies carried out on a large number of present-day, as well as fossil diatom frustules. From the diffraction patterns given by the various specimens, it has been concluded that the silica present in diatom frustules is not in an amorphous or sub-colloidal state as was spposed by previous workers but that it is crystalline α-quartz. Although crystalline α-quartz is present in present-day diatoms, the degree of crystallisation is much less than in the fossilized specimens. In addition to the crystalline quartz content, there is present in all diatoms an organic component which might possibly be a protein. In the present-day diatoms this organic component occurs in considerable proportion so that its X-ray diffraction pattern tends to mask the pattern due to crystalline α-quartz. On fossilization, however, a considerable amount of the protein content is lost, while the silica content becomes more predominant, and more and more crystalline with time. Evidence for the occurrence of pectin in diatoms is also presented.