How do flake salt crystals form in an open grainer?

In an open grainer, flake salt crystals form through a specific process of surface evaporation. The grainer, which is a long open trough heated by steam coils, is filled with settled and filtered brine.1

As evaporation occurs at the surface of the liquid, salt crystals originate there and are held up by the surface tension of the brine. Each crystal grows at its top edges, eventually forming a small, inverted hollow pyramid known as a hopper. Once these hoppers become heavy enough, they sink and cease to grow. Because the salt is recovered from these surface-grown crystals, the resulting product is characterized by its flake-like form.1