To mineralogists rock-salt is often known as halite - a name suggested in 1847 by E.
The word halite, however, is sometimes used not only for the species rock-salt but as a group-name to include a series of haloid minerals, of which that species is the type.
Halite or rock-salt crystallizes in the cubic system, usually in cubes, rarely in octahedra; the cubes being solid, unlike the skeleton-cubes obtained by rapid evaporation of brine.
Halite occasionally exhibits double refraction, perhaps due to natural pressure.
Pure halite consists only of sodium chloride, but salt usually contains certain magnesium ccmpounds rendering it deliquescent.
Halite may occur as a sublimate on lava, as at Vesuvius and some other volcanoes, where it is generally associated with potassium chloride; but its usual mode of occurrence is in bedded deposits, often lenticular, and sometimes of great thickness.