Quartz with Cinnabar

Mineral aggregate

SiO2 with HgS

Also known as: Cinnabar in Quartz, Mercury Ore in Quartz

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Description

Quartz with Cinnabar is a mineral aggregate consisting of quartz (silicon dioxide, SiO2) and cinnabar (mercury sulfide, HgS). The quartz typically forms as clear, milky, or smoky crystals, or as massive chalcedony, providing a matrix or host for the vibrant red to reddish-brown cinnabar. Cinnabar often occurs as disseminated grains, crystalline coatings, or distinct euhedral to subhedral crystals within or on the quartz. The striking contrast between the often translucent or transparent quartz and the opaque, vivid red cinnabar makes these specimens visually distinctive. The presence of cinnabar indicates a mercury-rich hydrothermal system.

How to Identify

Color: Quartz can be colorless, white, milky, smoky, or amethystine. Cinnabar is typically vermilion red, reddish-brown, or scarlet. The combination presents a striking red against a lighter background.
Luster: Quartz has a vitreous (glassy) luster. Cinnabar has an adamantine (diamond-like) to sub-metallic luster, sometimes dull in massive forms.
Texture: Quartz can be crystalline (euhedral to anhedral crystals), massive, or cryptocrystalline (chalcedony). Cinnabar can be granular, massive, or as distinct rhombohedral or tabular crystals.
Crystal Form: Quartz typically forms hexagonal prisms terminated by rhombohedra. Cinnabar forms trigonal crystals, often as rhombohedra, tabular, or prismatic forms, but is frequently massive or granular.
Cleavage: Quartz has no true cleavage, exhibiting conchoidal fracture. Cinnabar has perfect prismatic cleavage on {1010}.
Geological Environment: Low-temperature hydrothermal veins, hot spring deposits, and volcanic environments, often associated with fault zones and areas of active or recent volcanism.

Key Facts

Hardness: Quartz: 7 on Mohs scale. Cinnabar: 2-2.5 on Mohs scale.
Specific Gravity: Quartz: 2.65 g/cm³. Cinnabar: 8.0-8.2 g/cm³ (very dense).
Crystal System: Quartz: Trigonal. Cinnabar: Trigonal.
Color: Quartz: Colorless, white, milky, smoky, purple. Cinnabar: Vermilion red, reddish-brown, scarlet.
Luster: Quartz: Vitreous. Cinnabar: Adamantine to sub-metallic, sometimes dull.
Transparency: Quartz: Transparent to translucent. Cinnabar: Opaque to translucent.
Fracture: Quartz: Conchoidal. Cinnabar: Uneven to sub-conchoidal.
Cleavage: Quartz: None. Cinnabar: Perfect prismatic on {1010}.
Composition: Quartz: Silicon dioxide (SiO2). Cinnabar: Mercury sulfide (HgS).

Quick Check

Color: Red (cinnabar) on colorless, white, or smoky (quartz)
Luster: Vitreous (quartz) to adamantine/sub-metallic (cinnabar)
Streak: Scarlet red (cinnabar)

Physical Characteristics

Crystal Habit: Quartz: Prismatic, massive, granular, cryptocrystalline. Cinnabar: Rhombohedral, tabular, prismatic, massive, granular, earthy coatings.
Cleavage Type: Quartz: Absent. Cinnabar: Perfect prismatic.
Fracture Type: Quartz: Conchoidal. Cinnabar: Uneven to sub-conchoidal.
Tenacity: Quartz: Brittle. Cinnabar: Brittle.
Luster Type: Quartz: Vitreous. Cinnabar: Adamantine to sub-metallic.

Formation

Quartz with Cinnabar forms in low-temperature hydrothermal veins, typically in volcanic or hot spring environments. Cinnabar (HgS) precipitates from mercury-rich hydrothermal fluids, often in association with silica (SiO2) deposition. The silica can form as quartz crystals, chalcedony, or opal, encasing or intergrown with the cinnabar. This process occurs at relatively shallow depths and temperatures generally below 200°C, often in areas of active or recent volcanism and tectonic activity.

Usage

Historically, cinnabar was the primary ore for mercury extraction, which was used in thermometers, barometers, electrical switches, and chemical processes. It was also used as a pigment (vermilion). Quartz with cinnabar specimens are highly prized by mineral collectors due to their striking color contrast and the rarity of well-formed cinnabar crystals. Due to the toxicity of mercury, its industrial uses have significantly declined, and mining of cinnabar is now heavily regulated or banned in many regions.

Age Distribution

Typically associated with relatively young (Cenozoic to Mesozoic) volcanic and hydrothermal activity, but can be found in older deposits.

Where to Find

Almadén, Spain

Historically the world's largest mercury mine, known for exceptional cinnabar specimens, often associated with quartz and dolomite.

Idrija, Slovenia

Another historically significant mercury mining district, producing cinnabar in various matrices, including quartz.

Huancavelica, Peru

Known for its rich mercury deposits, where cinnabar is found in hydrothermal veins with quartz.

New Almaden, California, USA

A major mercury producer in the United States, with cinnabar occurring in quartz veins and breccias.

Guizhou Province, China

A significant source of high-quality cinnabar specimens, often found in association with quartz, calcite, and dolomite.

Terlingua, Texas, USA

Known for its mercury deposits, where cinnabar is found in veins and disseminated in sedimentary rocks, sometimes with quartz.

Finding Tips

Safety First

Cinnabar is a mercury sulfide and is toxic. Always handle specimens with gloves. Avoid inhaling dust, and do not ingest. Wash hands thoroughly after handling. Do not grind, cut, or heat cinnabar specimens, as this can release toxic mercury vapor. Store specimens in sealed containers away from children and pets.

Look for Hydrothermal Veins

Focus your search in areas known for low-temperature hydrothermal activity, especially near volcanic or hot spring systems. Cinnabar often forms in veins cutting through host rocks.

Identify Associated Minerals

Cinnabar is frequently found with other minerals such as pyrite, marcasite, stibnite, calcite, dolomite, and various forms of silica (quartz, chalcedony, opal). The presence of these minerals can indicate a favorable environment.

Color and Luster

The distinctive vermilion red color and adamantine luster of cinnabar are key identifiers. Look for these red specks or coatings within or on quartz crystals or masses.

Geological Maps

Consult geological maps of known mercury mining districts or areas with documented hydrothermal mineralization. These maps can pinpoint specific localities or geological formations likely to host cinnabar.

Similar Rocks

Realgar in Quartz

SiO2 with AsS

Also known as: Arsenic Sulfide in Quartz

Proustite in Quartz

SiO2 with Ag3AsS3

Also known as: Ruby Silver in Quartz

Cuprite in Quartz

SiO2 with Cu2O

Also known as: Copper Oxide in Quartz

Scientific Classification

Mineral Class: Quartz: Tectosilicate. Cinnabar: Sulfide.
Group: Quartz: Quartz Group. Cinnabar: Cinnabar Group (though often considered a standalone mineral due to its unique properties).
Crystal System: Trigonal for both.
Chemical Formula: SiO2 (Quartz) and HgS (Cinnabar)
Composition: Silicon dioxide and mercury sulfide.

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