Salt, NaCl, is essential to life, in a rather precarious balance - too much is bad and can kill you and too little is dangerous and can kill you as well. Salt without iodine is also an issue.
During the Roman Empire, salt was more precious than gold and Roman soldiers were paid in both coins and salt, salarium.
The Latin word for salt, salarium, gave us the English word, salary.
We can produce salt in three different ways:
1. We can evaporate it from the ocean in a painstaking process. The neolithic people in Boulby processed salt at scale thousands of years ago.
2. Rock salt can be mined from the ground, a process that is quite old too. For example, the Khewra salt mine in Pakistan dates back to Alexander the Great. This Khewra salt is sold under the name of Himalayan pink salt. The Khewra mine is not really that close to the Himalayan foothills; it is about 200 miles away.
In north-west Austria, the Hallein mine is so old that they found within it the skeleton of a Celtic miner who had been trapped there thousands of years ago. No longer exploited, this mine is now an exploratory cavern with its own funicular railway.
3. The least difficult way to exploit underground salt is to bring it up in the form of brine, without any humans ever setting foot in the mine. This is called "solution mining." Brine is brought up from underground with pressurized water. This solution has a 30 percent salt content. To get an idea of how much salt is in this brine, compare it to sea water which only contains 3 percent salt.
No dynamite or drills are used, just pressurized water.
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