Well-mined salt are inland water deposits, basically not with other minerals *** birth, that is to say, the place was a sea, then the sea water was buried by the crust, the water evaporated and left behind is the salt, so the salt mines are generally a large area of a few hundred meters thick layer of salt, which is not much of a mineral impurity.

Well mine salt are water mining method, in layman's terms, that is, in the salt layer in two tubes into, one into the water, the other out of the saturated brine (don't forget that salt is soluble in water), and then these saturated brine evaporated, you get salt.

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Difference between Well Salt and Sea Salt:

Sea Salt is a salt made from seawater by solarization, and processed sea salt may contain copper, iron, magnesium, calcium, and other trace elements, in addition to the main ingredient sodium chloride. The trace elements contained in sea salt of different origins are different, which will produce different colors, in addition to the common white, there are also yellow-brown, gray-brown, light red, dark white.

Well salt is processed using the well-drilling method, drawing on shallow surface or underground natural brine, and the processed well salt may contain other trace elements such as magnesium and calcium in addition to the main ingredient sodium chloride, and its color is generally white.

Baidu Encyclopedia - Well Salt