Aragonite observed in the prismatic layer of seawater-cultured pearls

Abstract

The prismatic layer is obviously different from the parallel layer in seawater-cultured pearls. X-ray diffraction (XRD), optical microscopy (OM) and micro-infrared (IR) spectroscopy have been applied to characterize the crystallized layers of high-and low-quality seawater-cultured pearls produced in South China. The result shows that the prismatic layer is not only composed of calcite as reported in previous researches. Three types of prisms were found in seawatercultured pearls: calcite prism, aragonite prism and calcite and aragonite prism. Therefore, we have a new understanding of the biomineralization of the prismatic layer in seawatercultured pearls. The result makes us review the traditional viewpoint that the increased content of aragonite improves the quality of pearls. We discovered that some seawater prismatic pearls almost completely composed of aragonite have the worst quality. We thought that the thickness and the spatial distribution of prisms are the main factors that can affect the quality of seawater-cultured pearls.

The role of matrix proteins in the control of nacreous layer deposition during pearl formation

“…During the middle stages (days [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], the carbon content decreased, as did the organic matrix and the baseline Raman spectrum. In previous studies, the CaCO 3 first deposited on the nucleus was the aragonitic [29] or calcitic [30] prismatic layer found in the cross section of the pearl, and the nacreous layer then formed on the prismatic layer. In the early stages in our study, the CaCO 3 depositions were all aragonites.…”

A modified integrated model of the internal structure of Chinese cultured pearls

“…Some of the pearls had an extraordinarily thin prismatic layer ( Fig. 5(a)) [12] while the others did not have any prismatic layer at all (Fig. 4).…”

“…Thick prismatic layers are the most signifi cant characteristic of these prismatic pearls as the crystallizing layers are essentially composed of these prismatic layers ( Fig. 5(b),(c),(d)) [12] . The prisms in these prismatic pearls are thicker than the fi ne needle-like prisms found in high quality pearls.…”

“…8. If there are prisms, they are calcite prisms [1] or aragonite prisms [12] or a combination of aragonite and calcite prisms [12] in seawater cultured pearls. They are aragonite prisms or vaterite prisms in freshwater cultured pearls [13] .…”

Pearl formation in the Japanese pearl oyster ( Pinctada fucata ) by CaCO 3 polymorphs: Pearl quality‐specific biomineralization processes and their similarity to shell regeneration

“…In such pearls, the prismatic layer on the nucleus differs from that of shell with respect to the crystal habit (Komaru, Sato, & Inoue, ). For example, aragonite prismatic layers (Cuif et al, ; Ma et al, ), pseudo‐prisms (Pérez‐Huerta, Cuif, Dauphin, & Cusack, ) and prism‐like structures (Komaru et al, ; Wada, ) have been reported. Hereinafter, these columnar structures which resemble prismatic layer in pearls are together referred to as non‐nacreous structures (NNSs) in this study.…”