Mercury is a metal with several strange characteristics. It is liquid at average temperatures, it is rather heavy (13.6 g/cm³) and its colour is grey. It is also called quicksilver, as small amounts form little spheres because of their surface tension and roll very fast on the floor. Because of its big weight, iron bars swim on the liquid mercury.
Mercury is toxic. Unfortunately it tends to evaporate and the Mercury gas is extremely dangerous. The body is not able to get rid of mercury, after it is once incorporated, and so it builds up until heavy symptoms of an intoxication appear. Mercury intoxication is painful and often lethal.
Because of its exceptional characteristics, mercury is often found in a pure form. So it is possible to just collect it from fractures in the rock using a pipette. But this is very dangerous as the pure mercury evaporates and the atmosphere in the mine is toxic, at least if the miners work for years in there.
Also very common is the red cinnabar ore (mercury sulfide, HgS), which contains a very high amount of mercury. In this case the mining is less dangerous, but there is the need to heat the ore to extract the mercury. This results in a continuous need of wood, which lead to some nature destruction around mercury mines.
The liquid metal mercury is very important for modern industry. It is used for switches, for example in car alarm systems or bombs, it is used in thermometers and barometers to measure temperature or air pressure. It is also used by dentists in amalgam. But because of its dangers it is nowadays replaced by plastic or ceramic fillings.
Unfortunately mercury can be used to produce gold. In gold deposits with fine gold dust, the mercury is added in huge amounts and it collects the gold and allows to separate it from the other rocks. During this process a huge amout of mercury is lost and pollutes the surrounding area.
Also old mercury mines are a continuous threat to people living around. Groundwater dissolves mercury and other toxic substances from the rocks and brings it to the surface.