Wattersite
Chemical formula: Hg<sup>1+</sup><sub>4</sub>Hg<sup>2+</sup>O<sub>2</sub>(Cr<sup>6+</sup>O<sub>4</sub>)
Wattersite is a very rare mercury chromate, distinguished by its intense, black color and occurrence as small, lustrous crystals.
Properties
- Mohs hardness
- 3.5
- Luster
- Sub-Adamantine
- Streak
- Black
- Density
- 9.4
- Cleavage
- Good on {100}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Wattersite can be identified by its black color, strong submetallic or adamantine luster, and very high density. Its occurrence in association with other mercury minerals, especially in serpentinites, is key. Due to the microscopic size of the crystals, magnification is often required for identification. ## Distinguishing from Similar Minerals It can be confused with other black, heavy minerals. It is distinguished from magnetite by the absence of magnetic properties. It is distinguished from other oxides and sulfides by its specific genesis and co-occurrence with mercury minerals in low-temperature hydrothermal environments. ## Crystal Forms It forms very small, prismatic or tabular crystals, often with a hexagonal outline. They usually occur as dispersed, single crystals or small aggregates on the rock surface.
Geological environment
## Genesis Wattersite is a hydrothermal mineral, forming at low temperatures. It forms as a product of oxidation and alteration of mercury minerals in near-surface zones, within mercury deposits hosted in serpentinites. ## Mineral Associations This mineral occurs in association with other, often rare, mercury minerals. Most commonly, it co-occurs with cinnabar, native mercury, edgarbaileyite, dewalite, mercury-bearing cordierite, and minerals from the montroydite group. The host rock is usually serpentinite or fractured silica. ## Localities The only confirmed and well-described locality for wattersite in the world is its type locality – the Clear Creek mine in San Benito County, California, USA. This is one of the rarest mineralogical sites.
Rarity
Extremely rare
For collectors
## Quality Criteria Due to its extreme rarity, every authenticated wattersite specimen is valuable. Micromounts with well-formed, sharp, and lustrous crystals that contrast with the rock matrix are most highly prized. The size and abundance of crystals on a given rock fragment are key factors influencing value. Clarity is not a significant criterion, as the mineral is inherently opaque. ## Popular Localities The only source of collectible specimens is the type locality – the Clear Creek mine in California. Specimens from this location are highly sought after by collectors specializing in rare minerals ("rarity collectors") and minerals from specific localities.
Care and storage
## Cleaning Due to its extreme rarity, fragility, and toxicity, wattersite specimens should generally not be cleaned. Any mechanical or chemical intervention risks destroying the mineral and releasing toxic mercury. If dust removal is necessary, a very gentle stream of compressed air from a distance can be used. ## What to Avoid Avoid contact with water, acids, chemical agents, and ultrasound. The mineral is sensitive to elevated temperatures, which can cause its decomposition and the release of toxic mercury vapors. Avoid all forms of mechanical cleaning, including brushes. Direct skin contact must be avoided. ## Storage Wattersite specimens must be stored in sealed, closed containers, preferably transparent plastic (e.g., a micromount box), to allow observation without direct contact. The container should be clearly labeled as toxic material. Store in stable conditions, away from heat sources, sunlight, and out of reach of children and pets.