Rock salt is made of a 1:1 ratio of sodium to chlorine. Rock salt's chemical formula is NaCl, which means that one molecule of rock salt is composed of one atom of sodium (Na) and one atom of chlorine (Cl).
Rock salt is the common name for the mineral "halite." It is also known by its chemical name, sodium chloride, and is what is most commonly referred to as "table salt." In its solid form, each ion is surrounded by six other ions of the opposite charge. This is because rock salt is an ionic compound.