Here's why:

* Limestone is primarily made of calcium carbonate (CaCO3). It forms from the accumulation of marine organisms' shells and skeletons.

* Sodium chloride is the chemical compound that makes up table salt. It's found in seawater and some rock formations like evaporites, but not in limestone.

While limestone may contain trace amounts of other minerals, including some with sodium, the primary component of limestone is calcium carbonate, and it doesn't contain sodium chloride in significant amounts.