2017 · Q9
Pearl is a hard object produced within the soft tissues of a mollusk. Which one of the following is the main constituent of pearl ?
General KnowledgeBiology
- ACalcium carbonate
- BCalcium oxide
- CCalcium nitrate
- DCalcium sulphate
Explanation
A pearl forms when a mollusk secretes concentric layers of nacre (mother-of-pearl) around an irritant lodged in its soft tissue. Nacre is composed principally of calcium carbonate in its aragonite crystal form, cemented by the protein conchiolin. Calcium oxide, calcium nitrate and calcium sulphate are not constituents of pearls. The main constituent is therefore calcium carbonate.