Ariegilatite

Chemical formula: BaCa<sub>12</sub>(SiO<sub>4</sub>)<sub>4</sub>(PO<sub>4</sub>)<sub>2</sub>F<sub>2</sub>O

Ariegilite is a very rare phosphosilicate mineral, discovered in Israel, forming colorless, tabular crystals.

## Characteristics Ariegilite is an extremely rare mineral from the phosphosilicate group, approved by the IMA in 2013. It occurs as very small, colorless, tabular crystals, reaching up to 0.2 mm in size. These crystals are usually transparent and exhibit a vitreous luster. Due to its extreme rarity and small crystal size, it is a mineral known primarily within the scientific community and among specialized micromineral collectors. ## Physical Properties The mineral is characterized by a hardness of approximately 5 on the Mohs scale. Its density, calculated based on the chemical formula and unit cell parameters, is 3.83 g/cm³. The crystals have a vitreous luster and a white streak. It exhibits perfect cleavage in one direction. ## History and Name The mineral's name honors Arie Gil, an Israeli mineral collector who found the type material. Ariegilite was discovered in the Hatrurim Formation in Israel, known for the occurrence of many rare minerals formed under pyrometamorphic conditions. It was described by a team of mineralogists: Evgeny V. Galuskin, Irina O. Galuskina, Yevgeny Vapnik, Frank Gfeller & Thomas Armbruster.

Properties

Mohs hardness
5
Luster
Vitreous
Streak
White
Density
3.83
Cleavage
Perfect on {0001}
Fracture
Uneven
Transparency
Transparent
Crystal system
Trigonal

Diagnostic features

## Identification Identification of ariegilite is possible almost exclusively through advanced analytical methods, such as Raman spectroscopy, electron microprobe (EDS/WDS), and X-ray diffraction (XRD). Visually, it is indistinguishable from many other colorless, small minerals. The key factors are its occurrence location (Hatrurim Formation) and co-occurrence with other rare pyrometamorphic minerals. ## Distinguishing from Similar Minerals It can be confused with other colorless minerals from the Hatrurim Formation, such as calcite, aragonite, or other rare silicates and phosphates. Certain distinction requires specialized laboratory equipment. ## Crystal Forms It forms thin, tabular crystals with a hexagonal outline, often grouped into small aggregates.

Geological environment

## Genesis Ariegilite forms under pyrometamorphic conditions, meaning the alteration of rocks under very high temperature but low pressure. It is a product of the natural combustion of bitumens in the sedimentary rocks of the Hatrurim Formation. This process leads to the formation of a unique mineral assemblage that does not form under other geological conditions. ## Mineral Associations It co-occurs with other minerals characteristic of the Hatrurim Formation, such as larnite, brownmillerite, mayenite, and also gurimite, another rare barium phosphosilicate. ## Localities The only confirmed locality of ariegilite in the world is its type locality – the Hatrurim Formation near Arad in the Negev Desert, Israel.

Rarity

Extremely rare

For collectors

## Quality Criteria As a micromineral, ariegilite is valued primarily for its mere presence on the rock matrix. Specimens with well-formed, sharp, undamaged crystals that are clearly visible against the host rock are most highly rated. Crystal size, even if sub-millimeter, is crucial – the larger, the more valuable. The presence of associated minerals can increase the specimen's value. ## Popular Localities All known specimens come from a single location in the world – the Hatrurim Formation in Israel. This is a classic locality for collectors specializing in pyrometamorphic minerals.

Care and storage

## Cleaning Due to the extreme rarity and small size of the crystals, mechanical cleaning is not recommended and usually not necessary. Specimens should be protected from dust in specialized micromineral boxes. ## What to Avoid Avoid contact with chemicals, ultrasound, and extreme temperature changes. Despite a hardness of 5, brittle crystals are susceptible to mechanical damage. ## Storage Ariegilite specimens should be stored exclusively in designated "micromount" boxes to protect them from damage, dust, and loss. Avoid vibrations and shocks.

Sources

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