The opening image shows crystals of the mineral cinnabar, which is the most common mercury-containing ore. It is primarily composed of the compound mercuric sulfide, HgS. Cinnabar has been mined since the Stone Age for its uses as a pigment and as a source of pure mercury. Mercury can be easily harvested from cinnabar by roasting cinnabar powder (vermillion), which actually vaporizes the mercury metal. The hot mercury vapor can then be recondensed to yield pure liquid mercury.
Cinnabar is one of thousands of minerals that occur naturally on earth. Some minerals are common (like cinnabar) while others are rarer (like ores of gold and silver). Another less common mercury-containing mineral is montroydite, which is composed primarily of mercuric oxide (HgO). The composition of mercuric oxide was first determined in 1774 by the English chemist Joseph Priestley. Priestley showed that heating montroydite powder produced mercury metal and a gas, which he called phlogiston-free air. The gas was later determined to be oxygen. The revised name, based on information gained from experiments, allowed chemists to have a better understanding of chemical composition and chemical reactions. Clear unambiguous naming makes communication much easier and more reliable.
Opening image courtesy of Parent Géry. commons.wikimedia.org/wiki/File:Cinabre_macl%C3%A9_%28Chine%29_.jpg. Public Domain.