Mercury is a heavy, silvery metal that is liquid between -38 degrees Fahrenheit and 674 degrees Fahrenheit at normal atmospheric pressure. It is extracted by heating cinnabar, a red ore that is a compound of mercury and sulfur.
Mercury is toxic in all its forms, but it still has several common uses. It is used in mercury switches, where its ability to both flow and carry electrical current is useful. Its ability to expand in a predictable manner depending on temperature and pressure makes it useful in laboratory thermometers and barometers. Alloys of mercury, called amalgams, are used in tooth fillings. Mercury's ability to amalgamate with gold makes it useful for extracting gold from its ores.