Fabrièsite

Chemical formula: Na<sub>3</sub>Al<sub>3</sub>Si<sub>3</sub>O<sub>12</sub>·2H<sub>2</sub>O

Fabrièsite is a hydrated sodium aluminosilicate with a zeolite structure, named after mineralogist Jacques Fabriès.

## Characteristics Fabrièsite is a mineral from the zeolite group, approved by the IMA in 2017. It occurs as very small, colorless to white, hexagonal crystals in the form of plates or prisms, usually less than 20 micrometers in size. Due to its size, its visual characteristics are difficult to assess without advanced equipment, such as a scanning electron microscope. ## Physical Properties The crystals are too small to determine hardness, density, and other physical properties by traditional methods. The density calculated from the formula and unit cell parameters is 2.29 g/cm³. It exhibits weak, greenish cathodoluminescence. ## Colors and Varieties The mineral is colorless to white. No varieties have been distinguished. ## History and Name The mineral is named in honor of Jacques Fabriès (1932–2000), a French mineralogist and former director of the mineralogical laboratory at the Muséum National d'Histoire Naturelle in Paris, for his contributions to mineralogy. It was discovered in material from the Marcasite quarry in the Mount-Dore volcanic complex in France. ## Uses Fabrièsite has no known commercial or industrial applications. Its significance is purely scientific and collectible, although due to the microscopic size of its crystals, it is primarily of interest to specialized micromineral collectors.

Properties

Luster
Vitreous
Streak
White
Density
2.29
Cleavage
Perfect on {0001}
Transparency
Transparent to=
Crystal system
Hexagonal

Diagnostic features

## Identification Identification of fabrièsite is possible only through advanced analytical techniques, such as Raman spectroscopy, X-ray diffraction (XRD), and electron microprobe chemical analysis (EDS/WDS). Visual identification is impossible. ## Distinguishing from similar minerals Distinguishing it from other microscopic zeolites and aluminosilicates (e.g., gmelinite, chabazite, faujasite) requires specialized structural and chemical analysis. ## Crystal forms It forms hexagonal, tabular, or short prismatic crystals, often grouped into small aggregates. The crystals are usually too small for their form to be visible to the naked eye.

Geological environment

## Genesis Fabrièsite forms under hydrothermal conditions in the late stage of crystallization in voids and fissures of volcanic rocks, such as phonolites. It crystallizes from sodium- and aluminum-rich solutions at relatively low temperatures. ## Mineral associations This mineral occurs in association with other zeolite and hydrothermal minerals, such as analcime, natrolite, aegirine, nepheline, sanidine, and other rarer zeolites. ## Localities The only confirmed occurrence (type locality) is the Marcasite quarry, Puy de Marmant, Veyre-Monton, in the Mont-Dore volcanic complex, Auvergne, France.

Rarity

Extremely rare

For collectors

## Quality criteria As a micromineral, the value of a specimen is primarily determined by the quality and abundance of crystals visible under a microscope on the rock matrix, as well as the presence of well-defined crystallographic forms. Association with other rare minerals is also important. ## Popular localities The only source of specimens is the type locality in France, which makes them extremely rare and sought after by specialized micromineral collectors.

Care and storage

## Cleaning Due to the microscopic size and delicacy of the crystals, mechanical cleaning is neither recommended nor possible under amateur conditions. Specimens should be protected from dust. ## What to avoid Avoid contact with chemicals, ultrasound, and extreme temperature changes. As a mineral from the zeolite group, it may be sensitive to changes in humidity and dehydrate in dry environments, which can lead to structural damage. ## Storage Specimens should be stored in stable conditions, preferably in sealed "micromount" containers, which protect against dust, mechanical damage, and humidity fluctuations.

Sources

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