Chukhrovite-(Ca)

Chemical formula: Ca₃Ca₁.₅Al₂(S₆+O₄)F₁₃·₁₂H₂O

Chukhrovite-(Ca) is a rare calcium and aluminum sulfate-fluoride, forming colorless or white crystals in the isometric system.

## Characteristics Chukhrovite-(Ca) is a hydrated sulfate-fluoride belonging to the chukhrovite group. It occurs as well-formed, isometric crystals, most often in the form of octahedra, sometimes modified by cubes. Crystals are usually small, reaching up to several millimeters in size. This mineral is colorless, white, or yellowish and is characterized by a vitreous luster. ## Physical Properties Chukhrovite-(Ca) has a hardness of approximately 3.5 on the Mohs scale. It is a relatively light mineral, with a density of about 2.26 g/cm³. It is transparent to translucent. It does not exhibit cleavage, and its fracture is uneven to conchoidal. ## Colors and Varieties This mineral is most often colorless or white. It can take on a pale yellow coloration, likely due to impurities. No distinct color varieties or commercial varieties are recognized. ## History and Name Chukhrovite-(Ca) was described as a new mineral in 2004 by Oleg I. Siidra and his team. Its name refers to its chemical composition – the dominance of calcium (Ca) – and its relation to chukhrovite-(Ce), which was named after the Russian mineralogist Fyodor Vasilyevich Chukhrov (1908-1988). The type locality (locus typicus) is Tolbachik volcano in Kamchatka, Russia. ## Uses Chukhrovite-(Ca) has no industrial applications. It is solely an object of interest for collectors of rare minerals and scientists studying mineral-forming processes in volcanic environments.

Properties

Mohs hardness: 3.5
Luster: Vitreous
Streak: White
Density: 2.26
Cleavage: None
Fracture: Uneven to conchoidal
Transparency: Transparent to translucent
Crystal system: Isometric

Diagnostic features

## Identification Chukhrovite-(Ca) can be identified by its characteristic, isometric crystals with an octahedral habit, vitreous luster, and occurrence in a specific environment – volcanic exhalation zones. Its low hardness and density are also helpful features. ## Distinguishing from Similar Minerals It can be confused with other colorless minerals from fumarole zones, such as ralstonite or gearksutite. However, definitive differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS), due to visual similarity and small crystal sizes. ## Crystal Forms Crystals are typically isometric, mainly in the form of octahedra {111}, sometimes with cube faces {100}. It occurs as single, overgrown crystals or in small aggregates.

Geological environment

## Genesis Chukhrovite-(Ca) is a mineral of volcanic origin. It forms as a result of fumarolic activity, crystallizing from volcanic gases in exhalation zones. It is a product of sublimation at relatively low temperatures. ## Mineral Associations This mineral coexists with other fumarolic minerals, such as gypsum, anhydrite, ralstonite, jarosite, hematite, and tenorite. At the type locality on Tolbachik volcano, it was found in association with newly discovered and rare fluorides and sulfates. ## Localities The most important and best-documented occurrence of chukhrovite-(Ca) is its type locality – the fumarole field on the second cinder cone of the northern eruption of the Great Fissure of Tolbachik in Kamchatka, Russia. This is the only confirmed locality for this mineral worldwide.

Rarity

Very rare

For collectors

## Quality Criteria The most prized chukhrovite-(Ca) specimens are those with sharp, well-formed, and transparent crystals with a distinct luster. A contrasting matrix, such as hematite, significantly enhances visual appeal. Crystal size is a key factor – specimens with crystals exceeding 1-2 mm are considered exceptional. Purity (lack of inclusions) and absence of damage are also very important. ## Popular Localities The only source of collector specimens is Tolbachik volcano in Kamchatka. Material from this locality is extremely limited and appears on the market very rarely, mainly as a result of specialized mineralogical expeditions.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Due to possible water solubility, prolonged contact with liquids should be avoided. If washing is necessary, distilled water or isopropyl alcohol should be used, and the specimen should be dried immediately. ## What to Avoid Avoid contact with acids and other chemicals that can damage the mineral. Chukhrovite-(Ca) is relatively soft, so it must be protected from scratching by harder minerals. Ultrasonic cleaning devices should also be avoided. ## Storage Specimens should be stored in separate, padded boxes or display cases to prevent abrasion and mechanical damage. They should be protected from dust and moisture.

Sources

IMA Mineral List (CNMNC)