Cinnabar
Cinnabar is mercury sulphide, HgS: hexagonal, cochineal-red, scarlet streak, hardness 2 to 2.5, density 8.176. How to tell it from metacinnabar and cuprite.
Cinnabar is mercury sulphide, HgS: hexagonal, cochineal-red with a scarlet streak, hardness 2 to 2.5 and density 8.176. The Handbook calls it the most common ore of mercury world-wide. The same HgS also forms metacinnabar and hypercinnabar, with black and dark black-purple streaks. A 2 cm cube of cinnabar, worked, weighs 65.41 g, more than galena.
In short
- The identity card, from the Handbook of Mineralogy sheet: HgS, hexagonal, rhombohedral crystals to 10 cm, cochineal-red towards brownish red and lead-grey, streak scarlet, hardness 2 to 2.5, measured density 8.176, perfect {10-10} cleavage, slightly sectile. The September 2026 IMA-CNMNC Master List lists it as grandfathered, year ?, country unknown.
- Three minerals, one formula. A regex over the IMA list for rows whose formula is exactly HgS returns three: cinnabar, metacinnabar (G, 1870, USA) and hypercinnabar (A, 1977 s.p., USA). Only cinnabar has a red streak; metacinnabar’s is black, hypercinnabar’s dark black-purple.
- The scarlet-and-heavy rule. Of the six minerals in the table below, cinnabar is the only one with a scarlet streak, and the only one denser than 8. Cuprite’s streak is brownish red at 6.14; hematite’s cherry-red or reddish brown at 5.26; realgar’s red-orange at 3.56.
- Heavier than galena, worked. A 2 cm cube weighs 65.41 g as cinnabar, against 60.64 g for galena at 7.58. A 20.00 g piece weighs 17.55 g in water, the figure on the live realgar page.
- Toxicity is a separate page. What cinnabar contains and what that means is on is cinnabar toxic. This page identifies the mineral and gives no health, safety or handling advice.
| Mineral | IMA formula | Crystal system | Hardness | Density (measured) | Colour | Streak | 20.00 g piece in water | 2 cm cube |
|---|---|---|---|---|---|---|---|---|
| Cinnabar | HgS | Hexagonal | 2 to 2.5 | 8.176 | Cochineal-red, towards brownish red and lead-grey | Scarlet | 17.55 g | 65.41 g |
| Metacinnabar | HgS | Cubic | 3 | 7.65 | Greyish black | Black | 17.39 g | 61.20 g |
| Hypercinnabar | HgS | Hexagonal | 3 | 7.43 | Black with purple cast | Dark black-purple | 17.31 g | 59.44 g |
| Cuprite | Cu2O | Cubic | 3.5 to 4 | 6.14 | Cochineal-red, ruby-red, purplish red, to nearly black | Brownish red, shining | 16.74 g | 49.12 g |
| Hematite | Fe2O3 | Hexagonal | 5 to 6 | 5.26 | Steel-grey, dull to bright red | Cherry-red or reddish brown | 16.20 g | 42.08 g |
| Realgar | AsS | Monoclinic | 1.5 to 2 | 3.56 | Red to yellow-orange | Red-orange to red | 14.38 g | 28.48 g |
What is cinnabar? Mercury sulphide, as the sheet records it
HgS, essentially pure. The Chemistry field of the Handbook of Mineralogy sheet reads, in full, Essentially pure HgS. The IMA list prints the same formula, status G, with the year as a question mark and the country unknown. The mercury fraction by mass is worked on is cinnabar toxic and not repeated here.
Its crystal class. The sheet gives point group 32 and space group P3121 or P3221, the same pair the quartz sheet gives for quartz. Crystals are rhombohedral to 10 cm, thick tabular on {0001}, or stout to slender prisms parallel to [10-10]; twins are simple contact twins on {0001}. The bars on the four-index forms were read from the rendered sheet, and each satisfies h + k + i = 0.
Optics, worked. The sheet gives ω 2.905 and ε 3.256 at 598.5 nm, uniaxial positive. The difference, the birefringence, is 0.351. The lustre is adamantine, inclining to metallic when dark; dull in friable material. The name is from the Medieval Latin cinnabaris, traceable to the Persian zinjifrah, apparently meaning dragon’s blood, for the red color.
Cinnabar, metacinnabar or hypercinnabar? Three minerals, one formula
Method: a regex over the IMA list for rows whose formula column is exactly HgS. It returns three: cinnabar; metacinnabar, G, 1870, USA; and hypercinnabar, A, 1977 s.p., USA. The cinnabar sheet records them as trimorphous: one composition, three structures.
What separates them in the hand. Metacinnabar is cubic, in the sphalerite group, greyish black with a black streak, hardness 3 and density 7.65. It is commonly massive; rarely as small (to 1 mm) tetrahedral crystals. Its type locality on its sheet is the Redington mine, Napa Co., California. Hypercinnabar is black with a purple cast, streak dark black-purple, hardness 3, density 7.43, and intimately associated with metacinnabar, which it generally resembles. Its sheet gives two localities, the Mt. Diablo mine, California [TL], and the White Caps mine, Nevada.
A dark specimen labelled cinnabar is therefore worth a streak. The cinnabar sheet allows a lead-grey colour, but its streak is scarlet; a black streak points to metacinnabar or hypercinnabar. The metacinnabar sheet’s Uland analysis has 11.72% cadmium; worked, mercury is still 68.4% of the metal atoms, so it stays metacinnabar. The technique is on how to use a streak plate.
How to identify cinnabar: the scarlet-and-heavy rule
The rule: a scarlet streak and a density above 8 together mean cinnabar, among the six minerals in the table. Method: we read the Streak and D(meas.) fields of the six Handbook sheets. Cinnabar is the only scarlet and the only one above 8. It covers these six only, not every red mineral.
Why both tests. Streak alone leaves cuprite, brownish red, shining, and hematite, cherry-red or reddish brown, close enough to argue over. Density settles it: cinnabar is 1.33 times cuprite’s 6.14 and 1.55 times hematite’s 5.26. Hardness agrees: hematite is 5 to 6 and cuprite 3.5 to 4, against cinnabar’s 2 to 2.5. See cuprite and hematite.
Realgar is the soft red one. It shares cinnabar’s softness, 1.5 to 2, but at 3.56 it is 2.30 times lighter: a 2 cm cube weighs 28.48 g against 65.41 g. Its sheet records that it disintegrates on long exposure to light; the cinnabar sheet records nothing of the kind. See realgar. The weighing method is on how to measure specific gravity at home.
Where cinnabar is found: Almadén, Idrija, New Almaden and Hunan
The Distribution field calls cinnabar the most common ore of mercury world-wide, so only a few localities for exceptionally abundant or well-crystallized material can be mentioned. In Spain it names Almadén, Ciudad Real, and Mieres, Asturias; in Slovenia, Idrija (Idria); in Serbia, fine crystals at Mount Avala near Belgrade. In the USA it names New Almaden and New Idria, California; Terlingua, Texas; and the Cahill mine and Lovelock, Nevada.
China and Mexico. It lists Tongrin, Wanshanchang and elsewhere in Guizhou Province, and exceptional twinned crystals from the Tsar Tien mine, Hunan Province; also Charcas, San Luis Potosí, Mexico, and Hydercahn in the Fergana basin, Kazakhstan. It names no British locality, and we add none.
How it forms and with what. The Occurrence field: formed from low-temperature hydrothermal solutions in veins, and in sedimentary, igneous, and metamorphic host rocks. Associates: mercury, realgar, pyrite, marcasite, stibnite, opal, chalcedony, barite, dolomite and calcite. The rest of the reference section is at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.