Hypercinnabar
Chemical formula: HgS
It is a high-temperature, hexagonal polymorph of mercury sulfide (HgS), significantly rarer than its trigonal counterpart, cinnabar.
Properties
- Mohs hardness
- 3
- Luster
- Metallic
- Streak
- Black
- Density
- 7.76
- Cleavage
- None
- Fracture
- Conchoidal
- Transparency
- Opaque
- Crystal system
- Hexagonal
Diagnostic features
## Identification Identifying hypercinnabar is extremely difficult and usually impossible without advanced analytical methods, such as X-ray diffraction (XRD), which allows distinguishing its hexagonal structure from the trigonal structure of cinnabar. In collector's conditions, identification relies mainly on a label from a reliable source. Visual characteristics, such as black color, metallic luster, and high density, are only indications. ## Distinguishing from similar minerals Hypercinnabar is visually indistinguishable from metacinnabar (cubic variety of HgS) and some dark varieties of cinnabar (trigonal variety of HgS). Metacinnabar forms crystals in the cubic system (tetrahedra), while hypercinnabar crystallizes in hexagonal prisms and tabular forms. Cinnabar, although usually red, can be almost black, but its streak is always reddish, unlike the black streak of hypercinnabar. However, definitive differentiation requires structural analysis. ## Crystal forms It forms small, hexagonal crystals with a tabular or short-prismatic habit. It also occurs as granular aggregates, coatings, and as paramorphs after cinnabar crystals.
Geological environment
## Genesis Hypercinnabar is a hydrothermal mineral, crystallizing under low-pressure and relatively high-temperature conditions (above 344°C) from solutions rich in mercury and sulfur. It is a stable phase of mercury sulfide at higher temperatures than cinnabar and metacinnabar. During the cooling of the deposit, it transforms into cinnabar. ## Mineral associations It most often co-occurs with cinnabar (into which it transforms), metacinnabar, native mercury, pyrite, marcasite, stibnite, realgar, orpiment, calcite, barite, and quartz. ## Localities The most important and classic localities for this mineral are mercury deposits in California, USA, especially in the Mount Diablo and Knoxville areas. It is also known from several other locations worldwide, including Guizhou Province in China and Chiusdino in Italy. Everywhere it is a very rare mineral.
Rarity
Very rare
For collectors
## Quality criteria The most prized by collectors are specimens with well-formed, sharp crystals with a distinct hexagonal outline. An aesthetic composition with associated minerals, such as red cinnabar or shiny quartz, is also important. Due to its rarity, even microscopic but well-defined crystals achieve significant value. Confirmation of identification by an analytical laboratory significantly increases the specimen's value. ## Popular localities By far the most sought-after and classic specimens come from localities in California, USA (Mount Diablo, Contra Costa County, and Knoxville mine, Napa County). These are considered type material for this mineral.
Care and storage
## Cleaning Hypercinnabar specimens should only be cleaned mechanically, using a soft brush to remove dust. Water and any chemical agents should be avoided. Due to the toxicity of mercury, all operations should be performed with great care, preferably with gloves, and hands should be thoroughly washed after contact with the mineral. ## What to avoid The mineral is sensitive to elevated temperatures. Ultrasonic cleaners, chemical agents, acids, and detergents should be avoided. It should not be heated, as this can lead to the release of toxic mercury vapors. ## Storage Hypercinnabar should be stored in a closed, airtight container (e.g., a "membrane box"), away from other minerals to prevent potential contamination. It should be kept in a dry, cool, and dark place, out of reach of children and pets. The label should include a warning about toxicity.