Faujasite-Mg

Chemical formula: (Mg,Na,K,Ca)<sub>2</sub>(Si,Al)<sub>12</sub>O<sub>24</sub>·15H<sub>2</sub>O

Faujasite-Mg is a rare mineral from the zeolite group, the magnesium analogue of faujasite-Na, forming microscopic, octahedral crystals.

## Characteristics Faujasite-Mg is a hydrated magnesium, sodium, potassium, and calcium aluminosilicate, belonging to the zeolite group. It is the magnesium analogue of the much more common faujasite-Na. It forms very small, colorless or white crystals, most often in the form of regular octahedra, which rarely exceed 0.1 mm in size. For this reason, it is a mineral impossible to identify with the naked eye and requires advanced analytical techniques. ## Physical properties Faujasite-Mg crystals exhibit a vitreous luster. Due to the microscopic size of the crystals, properties such as hardness, density, cleavage, or fracture have not been precisely determined for natural samples and are only estimated based on analogy with synthetic counterparts and other faujasites. Hardness is estimated at approximately 4.5 on the Mohs scale, and density at approximately 1.93 g/cm³. ## Colors and varieties This mineral is usually colorless or white. No colored or commercial varieties are distinguished. ## History and name Faujasite-Mg was recognized as a distinct mineral species by the International Mineralogical Association (IMA) in 1997. Its name comes from the dominant magnesium (Mg) in its composition and refers to its connection with the faujasite structure. The original name "faujasite" honors the French geologist and volcanologist Barthélemy Faujas de Saint-Fond (1741-1819). ## Applications Natural faujasite-Mg has no commercial application due to its rarity and microscopic size. However, its synthetic counterparts, known as Y-type zeolites, are of immense industrial importance as catalysts in the catalytic cracking process in petroleum refineries.

Properties

Mohs hardness
4.5
Luster
Vitreous
Streak
White
Density
1.93
Cleavage
None
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Cubic

Diagnostic features

## Identification Identification of faujasite-Mg is impossible without specialized equipment. It requires chemical analysis (e.g., using an electron microprobe - EDS/WDS) to confirm the dominance of magnesium over sodium and calcium, and X-ray diffraction (XRD) to verify the FAU-type crystal structure. Visually, one can only observe typical, very small, sharp, and shiny octahedral crystals under high magnification. ## Distinguishing from similar minerals Faujasite-Mg is visually indistinguishable from other minerals in this series: faujasite-Na and faujasite-Ca. All form identical, colorless octahedra. Differentiation is possible only based on chemical composition analysis. It is distinguished from other microscopic zeolites by its characteristic, regular octahedral form. ## Crystal forms Faujasite-Mg crystallizes almost exclusively as simple, sharp, single crystals in the form of an ideal octahedron ({111}). Crystals are usually overgrown on the surface of other minerals and rarely form larger aggregates.

Geological environment

## Genesis Faujasite-Mg is a secondary mineral, forming at low temperatures as a result of hydrothermal activity or diagenesis. It forms in vesicles and cavities in volcanic rocks, such as basalts and phonolites, where it crystallizes from solutions rich in silica, aluminum, and magnesium. It can also form in sedimentary rocks, e.g., in volcanic tuffs that have undergone alteration in alkaline lake environments. ## Mineral associations This mineral coexists with other zeolites, such as phillipsite, chabazite, gismondine, as well as calcite and minerals from the smectite group (e.g., montmorillonite). ## Localities The most important and best-documented locality, which is also the type locality, is the Udersberg quarry near Daun in the Eifel mountains (Rhineland-Palatinate, Germany). It is found there in basalt vesicles. Other confirmed occurrences include the volcanic complex on Fuerteventura island (Canary Islands, Spain).

Rarity

Very rare

For collectors

## Quality criteria The quality of a faujasite-Mg specimen, a typical mineral for collectors specializing in "micromounts," depends on several factors. Most important is the sharpness and geometric perfection of the microscopic octahedral crystals. Specimens with numerous, well-formed crystals that are clearly separated and exposed on a contrasting matrix are more highly valued. The size of the crystals, even if we are talking about fractions of a millimeter, also matters – the larger, the more desirable the specimen. Purity and lack of damage are crucial. ## Popular localities By far the most valued and sought-after specimens by collectors come from the type locality – the Udersberg quarry in Germany. This is the classic and practically only source of well-formed microcrystals of this mineral on the collector's market.

Care and storage

## Cleaning Specimens with faujasite-Mg microcrystals should only be cleaned with compressed air to remove dust. Due to their extreme delicacy and small size, any mechanical contact (brushes, cloths) or cleaning with liquids (even water) is highly risky and can destroy the crystals. ## What to avoid Avoid contact with all chemicals, including acids and bases, which can destroy the zeolite structure. Ultrasonic cleaners should also be avoided. The mineral is sensitive to high temperatures, which can cause the loss of water from its crystal structure (dehydration) and its destruction. ## Storage Specimens should be stored in sealed, stable containers (e.g., "micromount" type) to protect them from dust, mechanical damage, and sudden changes in humidity. Storage in a dry place is crucial for maintaining structural stability.

External references

Sources

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