Cinnabar (German Zinnober), sometimes written cinnabarite, is a name applied to red mercury(II) sulfide (HgS), or native vermilion, the common ore of mercury. The name comes from the Greek, used by Theophrastus, and was probably applied to several distinct substances. Other sources say the word comes from the Persian zinjifrah, originally meaning “lost”.
Cinnabar was mined by the Roman Empire for its mercury content and it has been the main ore of mercury throughout the centuries. Some mines used by the Romans are still being mined today. It is generally found as a vein-filling mineral associated with recent volcanic activity and alkaline hot springs.
Cinnabar is generally found in a massive, granular or earthy form, and is bright scarlet to brick red in color. However, it occasionally occurs in crystals with a metallic adamantine luster. The crystals belong to the rhombohedral (trigonal) system, and are generally of rhombohedral habit, sometimes twinned. The twinning in cinnabar is distinctive and forms a penetration twin that is ridged with six ridges surrounding the point of a pryamid. It could be thought of as two scalahedral crystals grown together with one crystal going the opposite way of the other crystal.
Cinnabar presents remarkable resemblance to quartz in its symmetry and optical characteristics. Like quartz, it exhibits circular polarization, and Alfred Des Cloizeaux showed that it possessed fifteen times the rotatory power of quartz. It has higher refractive power than any other known mineral, its mean index for sodium light being 3 ~O2, while the index for diamond — a substance of remarkable refraction — is only 2~42. The hardness of cinnabar is 2 – 2.5, and its specific gravity 8.998.
Cinnabar is found in all localities which yield mercury, notably Almaden (Spain), New Almaden (California), Idrija (Slovenia), Landsberg, near Ober-Moschel in the Palatinate, Ripa, at the foot of the Apuan Alps (Tuscany), the mountain Avala (Serbia), Huancavelica (Peru), and the province of Kweichow in China, where very fine crystals have been obtained. Cinnabar is still being deposited at the present day from the hot waters of Sulphur Bank, in California, and Steamboat Springs, Nevada.
Hepatic cinnabar is an impure variety from Idrija in Carniola, in which the cinnabar is mixed with bituminous and earthy matter.
Metacinnabarite is a cubic form of mercury(II) sulfide, this compound being dimorphous.
Cinnabar may be associated with elemental (liquid) mercury and thus be dangerous to handle. Body temperature is often enough to vaporize the mercury out of the rock and this gas can be absorbed through the skin.