Halite

Halite is the mineral name for natural sodium chloride — common salt. It crystallizes in the cubic (isometric) system, forming distinctive cube-shaped crystals with perfect cubic cleavage, and is one of the few minerals readily identified by taste.

Most halite is colorless or white, but trace impurities and crystal defects produce grey, yellow, pink, and occasionally striking blue or purple specimens. It is soft, brittle, and dissolves readily in water.

Vast bedded deposits of halite occur worldwide, formed where ancient seas and salt lakes evaporated, leaving thick layers of salt sometimes hundreds of meters thick.

Halite is an evaporite mineral: it precipitates when bodies of saltwater — restricted seas, lagoons, and desert salt lakes (playas) — evaporate faster than they are replenished. As the brine concentrates, less soluble minerals like gypsum drop out first, followed by halite, then highly soluble potassium-magnesium salts.

Over geologic time these evaporite cycles build thick bedded salt deposits, often interlayered with gypsum, anhydrite, and clay. Because salt is low-density and flows plastically under pressure, deep beds can rise as salt domes that trap petroleum.

Classic deposits occur in Poland (Wieliczka), Germany, the US Gulf Coast, the Khewra mine in Pakistan, and dry lakebeds like Utah's Bonneville flats.

The most reliable tests are taste (distinctly salty), softness (Mohs 2-2.5, scratched by a fingernail), and perfect cubic cleavage — broken pieces form little cubes. Crystals are commonly cube-shaped, sometimes with stepped 'hopper' faces.

Halite is water-soluble (it dissolves and feels slick when wet), has a vitreous luster, and a white streak. Specimens are often grey, pink, or clear.

Look-alikes: Sylvite (potassium chloride) looks identical but tastes bitter rather than purely salty. Calcite is harder and fizzes in acid. Fluorite is much harder (4) and does not dissolve or taste salty.

Halite is the source of table and industrial salt, essential for food seasoning and preservation and as the raw material for chlorine, sodium hydroxide, and soda ash in the chemical industry.

Enormous tonnages are mined as rock salt for de-icing winter roads. It is also used in water softening, agriculture, and livestock licks.

Decoratively, pink Himalayan salt (a halite variety) is carved into lamps and slabs. In metaphysical use, salt is associated with cleansing and protection. Display specimens, especially blue and pink crystals, are collected, though they must be kept dry.