# Vaterite found in saltwater natural pearls from Pinctada Sp. mollusks

## TL;DR

This study found vaterite, a rare form of calcium carbonate, in natural saltwater pearls from Pinctada mollusks in the Persian Gulf, showing it can form in marine environments.

## Contribution

First conclusive identification of vaterite in natural saltwater pearls from marine bivalve mollusks.

## Key findings

- Vaterite was detected on the surfaces and cross-sections of saltwater pearls from Pinctada species.
- One pearl showed a predominantly vaterite structure with a calcite core.
- Vaterite can form in marine mollusks, not just freshwater mussels as previously known.

## Abstract

In this study, we report the detection of vaterite in natural saltwater pearls reportedly found inside Pinctada species mollusks, collected from the pearl oyster beds near the water of Kuwait in the Persian (or Arabian) Gulf. This rare polymorph of calcium carbonate was found on both surfaces and/or cross-sectional areas. Raman spectroscopy and X-ray diffraction (XRD) analyses were carried out in order to characterize the structures, which confirmed the presence of vaterite. The results of one pearl are detailed in this article, which showed a predominantly vaterite formation with a calcite central core. Our results showed that vaterite not only existed in freshwater cultured pearls grown in freshwater mussels as previously reported but also can be found in pearls from marine bivalve mollusks. To the best of our knowledge, this is the first time vaterite was conclusively identified in saltwater pearls and pearls of natural origin, and such information provided invaluable insights into biomineralization of calcium carbonate in these unique biogenic gem materials.