Question: what is the difference between calcium carbonate and limestone?
Answer: "Limestone" means any rock formed mostly of calcium carbonate (CaCO3), but to geologists, limestone is only one of several types of "carbonate rocks." These rocks are composed of more than 50% carbonate minerals, generally the minerals calcite (pure CaCO3) or dolomite (calcium-magnesium carbonate, CaMg[CO3]2) or both.