Pearl is a hard object produced within the soft tissues of a mollusk. Which one of the following is the main constituent of pearl?

Pearls are biogenic structures produced within the soft tissues of mollusks, primarily composed of calcium carbonate (CaCO3). This mineral exists in pearls in two main crystalline forms: aragonite and calcite. Aragonite is the primary component of nacre, or 'mother of pearl', which is secreted by the mollusk in thin, overlapping layers to create the pearl's characteristic iridescence. These calcium carbonate crystals are held together by an organic matrix of proteins and polysaccharides, such as conchiolin. While other calcium compounds like calcium oxide (quicklime) and calcium sulphate (gypsum) exist in nature, they are not the constituents of pearls. Pearls are highly sensitive to acids because they are composed of calcium carbonate, which dissolves when exposed to acidic substances like vinegar. Therefore, calcium carbonate is the fundamental chemical constituent of a pearl.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 1: Chemical Reactions and Equations > Figure 1.3 > p. 6