Chloromenite
Chemical formula: Cu<sup>2+</sup><sub>9</sub>O<sub>2</sub>(Se<sup>4+</sup>O<sub>3</sub>)<sub>4</sub>Cl<sub>6</sub>
Chloromenite is a very rare copper selenite, forming characteristic emerald-green crystals in volcanic exhalation products.
Description
## Characteristics Chloromenite is a mineral from the selenite group, chemically a hydrated copper selenite with chlorine. It forms small but well-formed crystals with a tabular or platy habit, which often combine into fan-shaped or radial aggregates, frequently resembling a crescent or bow tie. Its most characteristic feature is its intense, emerald-green color, which makes it visually attractive despite its small size. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of about 2-3. It exhibits a vitreous luster, transitioning to adamantine on some surfaces. It is transparent to translucent. Despite its low hardness, it is a dense mineral, with a density of about 4.6 g/cm³, which is noticeable even in small specimens. ## Colors and Varieties Chloromenite occurs in shades of green, most often a vivid, emerald green, which can transition to yellowish-green hues. No color or commercial varieties are distinguished. ## History and Name The mineral's name, approved in 1997, comes from the Greek words *chloros* (green) and *meniskos* (crescent), which directly refers to its typical color and the form of its crystal aggregates. It was discovered and described based on material from the fumaroles of the Tolbachik volcano in Kamchatka, Russia. ## Uses Due to its extreme rarity and small crystal size, chloromenite has no industrial applications. It is solely an object of scientific interest and a prized acquisition in advanced collections of rare and systematic minerals.
Diagnostic features
## Identification Key diagnostic features of chloromenite include its emerald-green color, tabular crystal habit, characteristic crescent-shaped or fan-like aggregates, and its specific occurrence environment – volcanic fumaroles. High density combined with low hardness is also a helpful characteristic. ## Distinguishing from Similar Minerals Chloromenite can be confused with other green, secondary copper minerals, such as atacamite, brochantite, or malachite. Differentiation based on visual characteristics can be difficult and often requires advanced studies (chemical analysis to detect selenium). The geological context and co-occurrence with other rare selenites (e.g., ilinskite, sofiite) are strong diagnostic indicators. ## Crystal Forms Crystals are most often thin-tabular, flattened parallel to the {010} plane. They frequently occur as fan-shaped, radial, or almost spherical aggregates. Single, isolated crystals are rare.
Geological environment
## Genesis Chloromenite is a mineral of volcanic origin, formed by sublimation from hot gases (exhalations) in fumaroles. It crystallizes at relatively high temperatures from gases rich in copper, selenium, and chlorine, depositing on the walls of fumarolic channels and in voids in lava. ## Mineral Associations This mineral co-occurs with other rare fumarolic minerals typical of its location. The most common associations include cotunnite, sofiite, ilinskite, georgbokiite, paratacamite, and halite. ## Localities The most important and type locality for chloromenite are the fumaroles of the Great Fissure Eruption of Tolbachik on the Tolbachik volcano (Kamchatka, Russia). This is its type locality (*locus typicus*). Its presence has also been confirmed in fumarole products on Mount Vesuvius in Italy.
Rarity
Very rare
Collector aspects
## Quality Criteria The highest valued chloromenite specimens are characterized by sharp, well-formed crystals with an intense, emerald color and high transparency. The form of aggregates is of great importance – symmetrical "bow ties" or fans are more desirable than chaotic clusters. Crystal size is crucial, although they rarely exceed a few millimeters. The value of a specimen is also enhanced by its placement on a contrasting matrix and its association with other rare minerals. ## Popular Localities The vast majority of the best quality chloromenite specimens available on the collector's market come from a single location in the world – the Tolbachik volcano in Kamchatka, Russia. Specimens from Vesuvius are extremely rare in collections.
Care and storage
## Cleaning Chloromenite specimens should only be dry-cleaned using a soft brush or compressed air from a safe distance. Contact with water is absolutely not recommended. ## What to Avoid This mineral is very sensitive to moisture and can be damaged or dissolved upon contact with water. All chemical agents, ultrasonic cleaners, and sudden temperature changes should be avoided. As a fumarolic mineral, it can be unstable in conditions of high air humidity. It should also be protected from direct sunlight. ## Storage It is recommended to store chloromenite in tightly sealed containers (e.g., "perky box" type) in a dry place with a stable temperature. Isolation from the environment protects it from moisture and contaminants that could react with it.