Step 1: Certain epidermal cells in plants like $Ficus$ enlarge and develop an internal outgrowth called a cystolith, and the cell housing this structure is termed a lithocyst.
Step 2: Chemically, the cystolith body is built up of calcium carbonate crystals deposited in layers around a cellulosic stalk projecting from the cell wall.
Step 3: Since the mineral deposit is calcium carbonate and not any of the other listed salts, that is the correct answer.