Cinnabar is mercury(II) sulfide, HgS, an identification with no serious historical dispute, since the mineral, the pigment, and the ore are demonstrably one and the same compound whether it occurs naturally as the red crystalline mineral or is synthesized directly from mercury and sulfur. What is worth noting for accuracy is that HgS exists in two structurally distinct forms, a stable red hexagonal crystal form, the familiar cinnabar and vermilion, and a metastable black cubic form sometimes called metacinnabar, produced under different conditions of formation or synthesis; the black form is the same substance discussed under this atlas's separate entry for aethiops mineral, and the two forms, chemically identical in composition but structurally different, were both known to alchemical practitioners even though they had no crystallographic vocabulary to describe the distinction they were plainly observing.
Chinese alchemical and pharmaceutical texts, working with cinnabar independently of the European and Islamic traditions, developed their own detailed accounts of its properties and its transformation into mercury remarkably early, a genuinely parallel line of practical chemistry worth noting alongside the more commonly cited Mediterranean sources. The clean and early metallurgical extraction of quicksilver from cinnabar by simple roasting, requiring no acid or complex reagent, made cinnabar one of the most economically important minerals of the pre-modern world wherever it was found in workable quantity.