Evanichite

Chemical formula: Pb<sup>2+</sup><sub>6</sub>Cr<sup>3+</sup>(Cr<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>(S<sup>6+</sup>O<sub>4</sub>)(OH)<sub>7</sub>FCl

Evanichite is an extremely rare mineral from the chromate group, distinguished by its intense orange-red color and complex chemical composition.

## Characteristics Evanichite is a very rare secondary mineral, occurring as microscopic, tabular crystals with a hexagonal outline. It forms thin coatings and crusts on the host rock. Its most characteristic feature is its intense, bright orange-red color. Due to its extreme rarity and small crystal size, it is a mineral of purely scientific and collector's interest. ## Physical Properties Evanichite crystals exhibit a vitreous luster. They are transparent to translucent. Hardness and density have not been precisely determined due to the small amount of available research material. ## Colors and Varieties This mineral occurs in a uniform, characteristic orange-red color. No varieties have been distinguished. ## History and Name Evanichite was approved as a new mineral species by the International Mineralogical Association (IMA) in 2023 (IMA2023-061). The name honors John Evanich, an American mineral collector from Arizona, who discovered the first specimens of this mineral and provided them for study. It was described by a team of mineralogists from the USA, including Anthony

Properties

Luster
Vitreous
Streak
Orange-red
Transparency
Transparent to translucent
Crystal system
Trigonal

Diagnostic features

## Identification Evanichite is primarily identifiable by its unique appearance: intense orange-red color, form of thin coatings, and occurrence in a specific geological environment. Final identification requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS). ## Distinguishing from Similar Minerals This mineral can be confused with other brightly colored chromates, such as crocoite or phoenicochroite. Differentiation is possible based on co-occurring minerals (e.g., the presence of lanarkite, leadhillite) and the form of occurrence – evanichite forms microscopic, hexagonal plates, while crocoite forms prismatic crystals. ## Crystal Forms Evanichite forms very small, thin, tabular crystals with a hexagonal outline. They occur as single plates or small aggregates forming coatings and crusts on the rock surface.

Geological environment

## Genesis Evanichite is a secondary mineral that forms in the oxidation zones of polymetallic deposits. Its crystallization is the result of complex hydrothermal processes occurring at low temperatures, in an environment rich in lead, chromium, sulfur, fluorine, and chlorine. ## Mineral Associations This mineral occurs in association with other rare secondary minerals. In the type locality (Evening Star mine), its co-occurrence with lanarkite, leadhillite, cerussite, wulfenite, anglesite, hemimorphite, and the newly described mineral adamsite-(Y) has been noted. ## Localities The only confirmed occurrence of evanichite in the world is its type locality – the Evening Star mine in Maricopa County, Arizona, USA. This is a small, historic mining site known for the occurrence of rare secondary minerals.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of evanichite specimens is primarily assessed based on the abundance and visibility of crystals on the rock matrix. Specimens with clearly formed, undamaged, hexagonal plates of intense color are most desirable. Due to the microscopic size of the crystals, the aesthetics of the entire aggregate and the contrast with surrounding minerals are crucial. ## Popular Localities The only source of evanichite specimens is the Evening Star mine in Arizona, USA. All materials available on the collector's market come from this single location.

Care and storage

## Cleaning Due to the extreme rarity and delicacy of specimens, mechanical cleaning is absolutely inadvisable. Any contaminants, such as dust, should be removed only with compressed air from a safe distance. ## What to Avoid Contact with water, chemicals, and ultrasound should be avoided. The mineral is likely sensitive to acids. It should be protected from high temperatures and direct, prolonged exposure to sunlight, which may cause it to fade. ## Storage Evanichite specimens should be stored under stable conditions, in closed, padded "micromount" boxes to protect them from mechanical damage, dust, and sudden changes in humidity. Display should be in a secured display case.

Sources

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