Mercury is usually produced from cinnabar rock, also known as mercury ore.
The rock contains mercury sulfide, which gives it its red color. To make pure mercury, you have to extract it from the cinnabar rock and eliminate the sulfur. The easiest way to do this is to heat the rock. The sulfur combines with oxygen and the mercury turns to vapor at a boiling point of 674 degrees F (356 degrees C). The vapor is condensed to form liquid mercury.
This video shows you the typical activities at a mine and during extraction: