Halite

Compound · NaCl

Elements

Crystal structure

One unit cell, the smallest block that repeats in every direction to build the whole crystal. Atoms on its faces, edges and corners are shared with the neighboring cells. Farther atoms are drawn fainter.
Cell: a = b = c = 5.64056 Å, all angles 90°
Space group: F m -3 m

Atom positions from the Crystallography Open Database entry 9008678 (Wyckoff, R. W. G., 1963).

Where it's found

Rock salt: thick beds left behind where ancient seas dried up, such as the Permian basins under Cheshire, northern Germany and West Texas, and the salt domes of the Gulf Coast, where buried salt has flowed upward through the rock above it. It also crusts modern salt flats and lakes like the Bonneville Salt Flats and the Dead Sea, and seawater is about 3.5% dissolved salt, most of it this.

How it's mined

Underground by room-and-pillar mining with continuous miners, as at Goderich in Ontario, the largest salt mine in the world, and Winsford in Cheshire; by solution mining, where water is pumped down a well to dissolve the salt and the brine is boiled down in vacuum pans; and by evaporating seawater or lake brine in shallow ponds under the sun. Most rock salt goes onto icy roads and into the chemical industry, which splits it into chlorine and sodium hydroxide.

Notes

Salt was mined at Wieliczka near Kraków from the thirteenth century until 1996, and the miners carved chapels, statues and chandeliers out of the salt as they went. The structure is the simplest one a crystal can have: sodium and chlorine alternate like the squares of a three-dimensional chessboard, every ion surrounded by six of the other kind. Galena has the same arrangement.