Dargaite

Chemical formula: BaCa₁₂(SiO₄)₄(S₆+O₄)₂O₃

Dargaite is an extremely rare mineral of the nabimusaite group, a complex barium and calcium silicate and sulfate, found in the Hatrurim Formation in Israel.

## Characteristics Dargaite is a silicate mineral. It forms small, anhedral (lacking characteristic crystallographic forms) or subhedral grains, usually not exceeding 100 micrometers in diameter. It occurs as inclusions in other minerals, mainly larnite. It is colorless, pale yellow, or pale brownish. ## Physical Properties The mineral is characterized by a vitreous luster and is transparent to translucent. Its Mohs hardness is approximately 5. The density, calculated based on the chemical formula and unit cell parameters, is 3.75 g/cm³. It does not exhibit cleavage, and its fracture is conchoidal. ## Colors and Varieties Dargaite is typically colorless to pale yellow. No colored varieties or trade names are known. ## History and Name The mineral was approved by the IMA in 2013. Its name comes from its discovery location – the Darga River valley in the Hatrurim Basin in Israel. It was described by a team of mineralogists led by Evgeny V. Galuskin. ## Uses Due to its extreme rarity and microscopic size, dargaite has no practical applications. It is solely an object of scientific and collecting interest for specialized micromineral collectors.

Properties

Mohs hardness: 5
Luster: Vitreous
Streak: White
Density: 3.75
Cleavage: None
Fracture: Conchoidal
Transparency: Transparent to Translucent
Crystal system: Trigonal

Diagnostic features

## Identification Visual identification of dargaite is impossible. Identification requires advanced analytical techniques, such as X-ray microanalysis (EDS/WDS) to determine chemical composition and X-ray diffraction (XRD) to confirm crystal structure. A key indicator is its occurrence in the specific geological environment of the Hatrurim Formation. ## Distinguishing from Similar Minerals Under a microscope, it can be confused with other colorless or light-colored minerals found in the same association, such as nabimusaite, larnite, or minerals from the apatite group. Definitive differentiation is only possible through chemical analysis, which will show the presence of barium, sulfur, and calcium in characteristic proportions. ## Crystal Forms Dargaite forms rounded, anhedral, or subhedral grains. Well-formed crystals are not observed. It occurs as inclusions in other minerals, mainly larnite.

Geological environment

## Genesis Dargaite forms under conditions of high-temperature, low-pressure contact metamorphism. It is a product of the alteration of carbonate rock xenoliths (limestones) within the pyrometamorphic rocks of the Hatrurim Formation (the so-called Mottled Zone). ## Mineral Associations This mineral co-occurs with other rare species characteristic of the Hatrurim Formation, such as nabimusaite, larnite, ye'elimite, brownmillerite, gehlenite, and anorthite. ## Localities The main and typical occurrence is the Hatrurim Basin in the Darga River valley in the Judean Desert, Israel. It has also been found in Jabel Harmun in the West Bank (Palestine), within the same geological formation.

Rarity

Extremely rare

For collectors

## Quality Criteria For such a rare micromineral as dargaite, the primary criterion for value is the certainty of identification, confirmed by analytical methods. Specimens rich in dargaite are prized, as are those where it co-occurs with other rare minerals from this locality, forming interesting parageneses. Grain size, though always microscopic, is also important – the larger the grains, the more desirable the specimen. ## Popular Localities The only known source of collectible specimens is the Hatrurim Formation in Israel and Palestine. Specimens from this locality are highly valued by collectors specializing in mineral systematics and minerals formed by pyrometamorphic processes.

Care and storage

## Cleaning Dargaite specimens are typically microminerals that do not require cleaning. If necessary, a gentle stream of compressed air can be used to remove dust. Avoid contact with water and chemical agents. ## What to Avoid Avoid ultrasonics, steam cleaners, acids, and all solvents. The mineral is sensitive to shock and abrasion, requiring careful handling. ## Storage Specimens should be stored in specialized micromount boxes to protect them from dust, moisture, and mechanical damage. Storage in stable room conditions is recommended.

External references

https://en.wikipedia.org/wiki/https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FDargaite