How dissolved salt becomes a rock
When seawater or salty lake water is trapped in a shallow basin, evaporation removes water but leaves dissolved minerals behind. As the brine grows more concentrated, sodium and chloride ions join into orderly, repeating structures. Halite crystals form, often with the small, flat faces and right-angled corners characteristic of their cubic structure.
If evaporation continues, crystals accumulate on the basin floor in layers. Later sediments can bury them, turning the deposit into a thick underground bed. In some places, buried salt slowly flows under pressure and rises through weaker rock, creating a dome-shaped mass called a salt dome.
A mineral name and a rock name
Halite is a mineral: a material with a characteristic chemical composition and crystal structure. “Rock salt” describes a rock made mostly of halite, though it can include other minerals or trapped impurities. The distinction is like the one between quartz and a quartz-rich rock: one names a mineral, the other a material made of it.
Food-grade salt is generally refined, so it may look and behave differently from a natural halite specimen; it can also contain small additions such as anti-caking agents. But the central ingredient is commonly sodium chloride. The geological name matters because it identifies not just what the material tastes like, but the crystal that can build vast layers beneath a basin—or grow as a clear cube in a hand sample.
