Minerals · common

Cinnabar

Cinnabar is mercury sulfide, HgS, the principal ore mineral of mercury and one of the most historically significant toxic minerals in human history. It forms a brilliant red to brownish-red mineral typically deposited by low-temperature hydrothermal fluids near volcanic activity and hot springs, often associated with recent or geologically young volcanic terrains. Cinnabar has been mined for millennia both for its metal content and, historically and dangerously, as a pigment source.

Photo: Robert M. Lavinsky · Wikimedia Commons · CC BY-SA 3.0

Cinnabar properties at a glance

Type	Minerals
Chemical formula	HgS
Mohs hardness	2–2.5
Crystal system	Trigonal
Luster	Adamantine to dull/earthy
Streak	Scarlet red
Cleavage	Perfect prismatic
Fracture	Uneven to subconchoidal
Specific gravity	8.0–8.2
Transparency	Transparent to opaque
Common colors	Red, Brownish red, Gray where tarnished
Rarity	common

Geology & background

Cinnabar precipitates from hydrothermal solutions circulating near active or recently active volcanic systems, typically at shallow depths and low temperatures where mercury-bearing vapors condense and react with sulfur to form the mineral in veins, breccias, and disseminated deposits. The Almadén district in Spain has been the world's most productive cinnabar locality for over two thousand years, while other major sources include the New Idria and New Almaden districts of California, Idrija in Slovenia, and Guizhou Province in China, which today accounts for much of global mercury production. These deposits are frequently associated with quartz, calcite, pyrite, and other low-temperature hydrothermal minerals.

Collectors should handle cinnabar specimens with care and wash hands after contact, since although solid cinnabar is far less hazardous than metallic or vapor-phase mercury, it should never be crushed, ground, or heated, as doing so can release toxic mercury compounds. Fine crystallized specimens showing sharp rhombohedral crystals are considerably rarer and more valuable than the massive, earthy material typically encountered, with Chinese localities in recent decades producing some of the finest crystallized cinnabar specimens on the market.

How to identify Cinnabar

Cinnabar displays a distinctive scarlet to brick-red or brownish-red color with an adamantine to dull luster and a diagnostic red streak that immediately sets it apart from most other minerals. It is notably soft at a hardness of 2 to 2.5, has perfect cleavage in one direction, and is unusually dense for a non-metallic-looking mineral due to its high mercury content. It can superficially resemble realgar or red hematite, but cinnabar's red streak differs from hematite's reddish-brown streak, and its much greater density and softness distinguish it from the arsenic sulfide realgar.

Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
Use multiple photos when possible, including a fresh surface and a close view of texture.

Where Cinnabar is found

Reported from multiple localities worldwide; verify locality against specimen provenance when available.

How much is Cinnabar worth?

Entry-level specimen	$2
Typical collector specimen	$20
Premium specimen	$150+

Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.

Common uses

Collector specimens
Education
Field identification
Industrial or lapidary use when suitable

Interesting facts

Ancient Romans and Chinese artisans ground cinnabar into vermilion pigment, prized for red lacquerware and paintings despite its toxicity.
Spain's Almadén mine produced an estimated one-third of all the mercury ever extracted throughout human history before closing in 2003.
Cinnabar's crystal structure is a low-temperature polymorph of mercury sulfide, while the black, metallic-looking form called metacinnabar represents a separate, denser structural arrangement of the same compound.