Edgarbaileyite

Chemical formula: Hg₁+₆Si₂O₇

Edgarbaileyite is a very rare mercury silicate, forming tiny, prismatic crystals with a characteristic adamantine luster.

## Characteristics Edgarbaileyite is an extremely rare mineral from the silicate group, chemically defined as mercury(I) silicate. It occurs as very small, prismatic or tabular crystals, rarely exceeding 1 mm in length. It typically forms small aggregates or coatings. It is transparent to translucent, and its most characteristic feature is an exceptionally strong, almost adamantine luster, which distinguishes it from other minerals. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 4. It has a very high density, approximately 7.1 g/cm³, which is a direct result of its high mercury content. Crystals exhibit perfect cleavage in one direction. Luster is one of its key diagnostic features – described as adamantine to almost metallic. ## Colors and Varieties Edgarbaileyite is usually colorless, white, light gray, or pale yellow. Some specimens may have a pale greenish or pale bluish tint. No named varieties of this mineral are distinguished. ## History and Name The mineral was discovered in the Clear Creek Mine in San Benito County, California (USA). It was described and approved as a new mineral species in 1990. Its name honors Edgar H. Bailey (1914–1983), an American geologist with the United States Geological Survey, who was a prominent specialist in the geology and mercury deposits of California. ## Uses Due to its extreme rarity, small crystal size, and toxic chemical composition, edgarbaileyite has no industrial applications. Its significance is purely scientific and collectible, being a coveted object for specialized collectors of rare minerals.

Properties

Mohs hardness: 4
Luster: Adamantine
Streak: White
Density: 7.1
Cleavage: Perfect on {100}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Key diagnostic features of edgarbaileyite include its extremely high density (the specimen is surprisingly heavy for its size), very strong adamantine luster, and occurrence in association with other mercury minerals. Reaction to light (darkening) is also a characteristic feature. However, final identification requires advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Edgarbaileyite can be confused with other colorless or pale yellow secondary minerals. It is distinguished from calcite by its much greater density and lack of reaction with hydrochloric acid. It is distinguished from some zeolites by its stronger luster and also significantly greater density. In the context of a mercury deposit, its luster and crystal form are quite unique. ## Crystal Forms Crystals are most often prismatic, elongated, and flattened, often with visible striations on the faces. They occur as single, scattered crystals or form small, radial aggregates and fan-shaped clusters on the surface of the host rock.

Geological environment

## Genesis Edgarbaileyite is a secondary mineral, forming in the oxidation zone of hydrothermal mercury deposits. It forms as a result of weathering and alteration of primary mercury sulfides (mainly cinnabar) in a silica-rich environment. Its formation is associated with serpentinite rocks. ## Mineral Associations This mineral co-occurs with other, often equally rare, mercury minerals. It is most commonly found in association with cinnabar, native mercury, calomel, eglestonite, wattersite, gianellaite, as well as with opal, quartz, calcite, and magnesite. ## Localities The most important and type locality for edgarbaileyite is the Clear Creek Mine in the New Idria district, San Benito County, California, USA. This is practically the only locality from which well-formed, collectible specimens of this mineral originate.

Rarity

Very rare

For collectors

## Quality Criteria The most prized edgarbaileyite specimens are those with sharp, well-formed, and transparent crystals that exhibit a strong luster. Crystal size is crucial – even specimens with crystals 1 mm long are considered exceptional. The attractiveness is enhanced by a contrasting, dark rock matrix and a rich association with other rare mercury minerals, such as red cinnabar or yellow wattersite. ## Popular Localities The only source of collectible specimens is the historical type locality – the Clear Creek Mine in California. This area is currently closed to collectors, which means that new specimens do not appear on the market, and the value of historical material increases.

Care and storage

## Cleaning Edgarbaileyite specimens should only be cleaned mechanically, with the utmost care, using a soft brush or compressed air to remove dust. Avoid contact with water and all chemicals. Due to its toxicity, all handling should be done with gloves. ## What to Avoid The mineral is sensitive to sunlight, which can cause it to darken or decompose. Contact with acids and other chemicals must be strictly avoided. Heating is extremely dangerous, as it leads to the release of toxic mercury vapors. It should be protected from moisture. ## Storage Specimens should be stored in a sealed, airtight container (e.g., a "perky box"), in a dark and dry place. It is essential to clearly label the container with a warning label indicating the toxic mercury content. Keep away from children and pets.

Sources

IMA Mineral List (CNMNC)