Aurivilliusite

Chemical formula: Hg₁+Hg₂+OI₁-

Aurivilliusite is an extremely rare mercury and iodine oxyhalide, forming microscopic, platy crystals of an intense red color.

## Characteristics Aurivilliusite is a mercury and iodine oxyhalide, occurring as extremely small, platy or bladed crystals, which rarely exceed 0.3 mm in length. It usually forms small aggregates or single, scattered crystals on the host rock. Its most characteristic features are its intense, red to reddish-orange color and adamantine luster. ## Physical Properties The crystals are very brittle and soft. Due to its extreme rarity and microscopic size, many physical properties, such as hardness or density, have not been precisely measured and are only estimated. The luster is described as adamantine to submetallic. ## Colors and Varieties This mineral occurs in a characteristic, bright range of colors from red, through reddish-orange to orange. No varieties are distinguished. ## History and Name Aurivilliusite was discovered in the Clear Creek mine in San Benito County, California, USA. It was described and approved as a new mineral species by the International Mineralogical Association (IMA) in 2000. The name honors the Swedish chemist and crystallographer Karin Aurivillius (1920–1982) for her pioneering research on mercury oxyhalides.

Properties

Mohs hardness: 2
Luster: Adamantine
Streak: Orange
Density: 8.25
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Aurivilliusite is identified based on its unique appearance: microscopic, platy crystals of a bright red color and adamantine luster, occurring in a specific geological environment. Due to its size, definitive identification requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS). ## Distinguishing from Similar Minerals It can be confused with other red secondary mercury minerals, such as cinnabar or eglestonite. However, cinnabar usually has a more granular or massive form and lower luster intensity. Eglestonite forms crystals in a different system (isometric) and has a different hue. Distinguishing it from other microscopic mercury oxyhalides (e.g., terlinguaite, poyarkovite) is impossible without laboratory analysis. ## Crystal Forms It forms very small, thin, platy or bladed crystals, often with a hexagonal outline. They occur as single, isolated crystals or small, loose aggregates on the rock surface.

Geological environment

## Genesis Aurivilliusite is a secondary mineral, forming in the oxidation zones of mercury deposits. It forms as a result of the weathering of primary mercury minerals, such as native mercury or cinnabar, in the presence of iodine-rich solutions. It occurs in vugs and fractures in siliceous-carbonate rocks. ## Mineral Associations At the type locality (Clear Creek mine), it co-occurs with native mercury, edgarbaileyite, eglestonite, cinnabar, calcite, quartz, and magnesite. ## Locations The only confirmed and described occurrence of aurivilliusite in the world is its type locality – the Clear Creek mine in the New Idria District, San Benito County, California, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of an aurivilliusite specimen is determined by the size and sharpness of the crystals, their number, and the intensity and purity of the red color. The most desirable specimens are those with well-formed, clearly visible crystals contrasting with the rock matrix. Due to its extreme rarity, any, even microscopic, specimen with confirmed identity is valuable to collectors specializing in rare or systematic minerals. ## Popular Localities The only source of specimens is historical finds from the Clear Creek mine in California, which is now closed and inaccessible. This means that no new specimens enter the market, and those available come exclusively from old collections.

Care and storage

## Cleaning Due to extreme brittleness, small crystal size, and solubility in acids, mechanical or chemical cleaning is absolutely inadvisable. Specimens should be left in their untouched state. ## What to Avoid Avoid contact with water, acids, and any chemicals. The mineral is very brittle, so avoid any shocks, friction, or touch. As a mercury mineral, it is toxic – avoid inhaling dust and direct skin contact. ## Storage Aurivilliusite specimens should be stored exclusively in closed, stable containers (e.g., "perky box" type) to protect them from mechanical damage and dust. They should be kept in a dry place, away from sources of vibration and direct sunlight. Always wash hands after handling the specimen.

Sources

IMA Mineral List (CNMNC)