Cinnabar

Cinnabar is mercury sulfide (HgS), instantly recognizable by its vivid scarlet to brick-red color. It is the principal ore of mercury and has been mined and used for thousands of years, both as a source of metallic mercury and as the red pigment vermilion.

Cinnabar typically occurs as granular masses, crusts, and coatings, with well-formed crystals being prized by collectors. Its brilliant red color and high density are distinctive.

Because it contains mercury, cinnabar is toxic and must be handled with care. It should never be heated or ingested, and dust from it should be avoided.

Cinnabar forms in low-temperature hydrothermal settings, typically near recent volcanic activity and hot springs. Mercury-bearing fluids deposit it in fractures, veins, and as impregnations in host rocks.

It commonly occurs with other low-temperature minerals such as pyrite, marcasite, quartz, opal, and stibnite. Deposits are often found in geologically young, tectonically active regions.

Famous localities include Almadén in Spain, the largest historic mercury source, as well as deposits in China, Italy, Peru, and the western United States. Native mercury sometimes occurs alongside cinnabar.

Cinnabar is identified by its bright scarlet-red color, adamantine to dull luster, very high density, and softness (hardness 2-2.5). Crucially, it gives a scarlet to red streak, a strong diagnostic feature.

Its great heaviness for a red mineral helps distinguish it from look-alikes like realgar (orange-red, also soft) and red minerals such as hematite (which gives a red-brown streak but is harder) and proustite. The combination of red streak, high density, and softness is distinctive.

Because cinnabar contains mercury, avoid creating dust, do not lick specimens to test streak, and wash hands after handling.

Historically, cinnabar was the world's primary ore of mercury, refined by roasting to release the liquid metal used in thermometers, scientific instruments, and gold extraction. It was also ground into vermilion, a brilliant red pigment for paint, lacquerware, and carvings.

Carved cinnabar (often actually red lacquer in Chinese decorative arts) has long been valued ornamentally. Today, due to mercury's toxicity, mining and pigment use have sharply declined.

Cinnabar remains a striking collector mineral, but specimens should be handled carefully because of their mercury content.