Nano-structured biogenic calcite: a thermal and chemical approach to folia in oyster shell.

The thin sheets of calcite in oyster shell in Crassostrea gigas are termed folia and comprise much of the oyster shell. The folia are covered by a layer of discrete globules that has been proposed to consist of aggregations of an organic matrix and minerals. A continuous organic framework divides each tablet into nanograins. Their shape is globular with a mean extension from 30 to 40 nm. Chemical and thermal treatments to correlate between the organic matrix and the minerals are considered using spectrometers, thermal analyzers, and electron microscopes. After treatment, the nanograins of the foliar and organic matrix are clearly identified. The organic matrix plays a key role in the thermal stability and material properties of this biological composite. From analysis of the FT-IR results, it is identified that the organic matrix in folia is composed of proteins and polysaccharides.