Salt mining

[2] As salt is a necessity of life, pre-industrial governments were usually keen to exercise stringent control over its production, often through direct ownership of the mines.

The Chinese writer, poet, and politician Zhang Hua of the Jin dynasty wrote in his book Bowuzhi how people in Zigong, Sichuan, excavated natural gas and used it to boil a rock salt solution.

[5] The Chinese made use of natural crystallization of salt lakes and constructed some artificial evaporation basins close to shore.

[5] Salt mining played a pivotal role as one of the most important sources of the Imperial Chinese government's revenue and state development.

This phrase originates from c. 1800 in reference to the Russian practice of sending prisoners to forced labor in Siberian salt mines.

Modern rock-salt mine near Mount Morris, New York
Diorama of an underground salt mine in Germany.
Inside Salina Veche , in Slănic, Prahova , Romania. The railing (lower middle) gives the viewer an idea of scale.
The Crystal Valley region of the Khewra Salt Mines in Pakistan . With around 250,000 visitors a year, the site is a major tourist attraction.
A small mosque made of salt bricks inside the Khewra Salt Mines complex
Large hole drilling rig for blast-hole drilling at salt mine Haigerloch -Stetten