Clearcreekite

Chemical formula: Hg¹⁺₃(CO₃)(OH)·₂H₂O

Extremely rare mercury(I) hydroxycarbonate, forming tiny, prismatic crystals and spherical aggregates with a silky luster.

## Characteristics Clearcreekite is a hydrated mercury(I) hydroxycarbonate, occurring as very small, colorless to white or pale yellow crystals. It typically forms radial or spherical aggregates, as well as bundles and rosettes of fine, acicular or prismatic crystals. Individual crystals rarely exceed 1 mm in length. Due to its chemical composition, it is a highly toxic mineral. ## Physical Properties Crystals exhibit a silky to pearly luster, which is characteristic of their fibrous structure. The mineral is soft, with a Mohs hardness of approximately 2. It is transparent to translucent. The density is high for a non-metallic mineral, around 6.26 g/cm³, which is typical for mercury-bearing minerals. ## Colors and Varieties Clearcreekite is usually colorless, white, or pale yellow. No named varieties of this mineral are recognized. ## History and Name The mineral was discovered in the Clear Creek Claim in San Benito County, California (USA), from which it derives its name. It was described and named in 1986 by Andrew C. Roberts, T. Scott Ercit, J. D. Grice, and Robert A. Gault. It was approved by the International Mineralogical Association (IMA) in the same year. ## Uses Clearcreekite has no industrial application. Its significance is purely scientific and as a collector's item, valued for its extreme rarity and origin from a unique mercury paragenesis.

Properties

Mohs hardness: 2
Color: Pale greenish yellow
Luster: Vitreous - Adamantine
Streak: Pale greenish yellow
Density: 0
Cleavage: {001} good
Fracture: Uneven
Transparency: Transparent
Crystal system: Monoclinic

Diagnostic features

## Identification Clearcreekite can be recognized by its occurrence in association with other mercury minerals, characteristic small, acicular crystals forming spherical or radial aggregates, and silky luster. High density is also an indicative feature, although difficult to measure on microscopic specimens. ## Distinguishing from Similar Minerals It can be confused with other secondary, acicular minerals from oxidation zones, such as gypsum or aragonite, but differs significantly from them by its much higher density and occurrence environment (mercury deposits). From other rare mercury minerals, it is distinguished by its chemical composition and characteristic crystal forms, requiring advanced analytical methods (XRD, EDS) for certain identification. ## Crystal Forms Crystals are prismatic, elongated, and often acicular. They usually occur as radial or spherical aggregates, as well as small bundles and rosettes.

Geological environment

## Genesis Clearcreekite is a secondary mineral formed in the oxidation zones of mercury deposits. It forms as a result of the weathering of primary mercury ores, especially native mercury and cinnabar, in the presence of carbonate-rich waters. It forms under low-temperature conditions, close to the Earth's surface. ## Mineral Associations This mineral co-occurs with other mercury minerals. In its type locality (Clear Creek Claim), it was found in association with native mercury, cinnabar, edgarite, calomel, eglestonite, terlinguaite, montroydite, as well as opal and magnesite. ## Localities The only confirmed and well-documented locality for clearcreekite in the world is its type locality - Clear Creek Claim, New Idria District, San Benito County, California, USA. This site is known for many other rare mercury minerals.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a clearcreekite specimen primarily depends on the richness and visibility of its crystals on the rock matrix. Specimens with well-formed, distinct radial or spherical aggregates that contrast with the substrate are most highly valued. The size of the aggregates, although always small, is also important – the larger and more numerous, the more valuable the specimen. Association with other rare mercury minerals is also significant. ## Popular Localities The only source of collector specimens is the historic Clear Creek Claim in California. This mine is currently closed and inaccessible, meaning no new specimens are entering the market. All available specimens come from old collections.

Care and storage

## Cleaning Clearcreekite specimens should generally not be wet cleaned. If absolutely necessary, compressed air can be used very carefully to remove loose dust. Due to its toxicity, all handling should be done with gloves and appropriate safety precautions. ## What to Avoid Avoid contact with water, acids, and other chemicals. The mineral is sensitive to temperature changes and mechanical shocks. Absolutely avoid inhaling dust or particles, as mercury is highly toxic. Do not heat the mineral. ## Storage Specimens should be stored exclusively in tightly sealed, clearly labeled containers (e.g., perky boxes) to prevent accidental contact and the spread of particles. Keep away from children, pets, and food. It is recommended to include a warning label about toxicity.