Explanation:

- Pearls primarily consist of calcium carbonate in the form of aragonite or calcite.

- Calcium carbonate is responsible for the lustrous appearance of pearls.

- Option 1: Calcium carbonate is correct, as it forms the bulk of the pearl's composition.

- Option 2: Calcium carbonate and magnesium is incorrect. Magnesium is not a significant component of pearls.

- Option 3: Calcium Sulphate is found in other minerals like gypsum but not in pearls.

- Option 4: Calcium Chloride is a separate compound used in different applications, unrelated to pearls.

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