Phosphoellenbergerite

Chemical formula: (Mg,&#₉₇₂₃;)₂Mg₁₂(PO₄,PO₃OH)₆(PO₃OH,CO₃)₂(OH)₆

A rare magnesium phosphate with a characteristic azure-blue coloration, found in high-pressure metamorphic rocks.

## Characteristics Phosphoellenbergerite is a very rare mineral from the phosphate group, being the phosphorus analog of ellenbergerite. It forms elongated, prismatic crystals, often with a hexagonal outline, which can reach several millimeters in length. It typically occurs as inclusions in other minerals, mainly in pyrope. Its most characteristic feature is its intense, azure-blue color. ## Physical Properties This mineral has a hardness of 6.5 on the Mohs scale, making it relatively scratch-resistant. It has a vitreous luster and a density of approximately 3.0 g/cm³. Crystals can be transparent to translucent. ## Colors and Varieties Phosphoellenbergerite occurs in one characteristic color: azure-blue. No color varieties or commercial forms are distinguished. ## History and Name The mineral's name refers to its chemical composition (dominance of phosphorus) and its relation to the kindred mineral, ellenbergerite. It was first described by Christian Chopin, Giancarlo Della Ventura, and Bruno Goffé in 1991. The type locality, from which the first described specimens originated, is the Dora-Maira Massif in the Italian Alps. ## Uses Due to its extreme rarity, phosphoellenbergerite has no industrial applications. It is solely an object of scientific and collecting interest.

Properties

Mohs hardness: 6.5
Luster: Vitreous
Streak: White
Density: 3.0
Transparency: Transparent,Translucent
Crystal system: Hexagonal

Diagnostic features

## Identification The key diagnostic feature of phosphoellenbergerite is its unique, azure-blue color, prismatic crystal habit, and specific occurrence environment – high-pressure metamorphic rocks. It is often visible as an inclusion within bright red or pink garnets (pyropes). ## Distinguishing from similar minerals Due to its characteristic color and paragenesis, it is difficult to confuse with other minerals. Within the Dora-Maira Massif, it can be mistaken for dumortierite, which, however, forms fibrous aggregates rather than individual, prismatic crystals. ## Crystal forms It forms well-developed, elongated prismatic crystals with a hexagonal cross-section. It usually occurs as single, isolated crystals, not in the form of aggregates.

Geological environment

## Genesis Phosphoellenbergerite is a mineral typical of rocks that have undergone metamorphism under very high pressure and relatively high temperature conditions. It forms in gneisses and quartz-pyrope schists, often in the presence of coesite, which indicates pressures exceeding 2.5 GPa. ## Mineral associations It most commonly co-occurs with pyrope (in which it forms inclusions), coesite, quartz, talc, kyanite, phengite, rutile, and jadeite. ## Localities This is an extremely rare mineral. The most important and best-documented locality is the type locality in the Dora-Maira Massif, in the province of Cuneo, Piedmont, Italy. This is the only place from which specimens of collecting significance originate.

Rarity

Very rare

For collectors

## Quality criteria The most highly valued specimens are those in which phosphoellenbergerite crystals are well-formed, have an intense, azure color, and are clearly visible as inclusions in transparent pyrope. The contrast between the blue of phosphoellenbergerite and the pink or red of the garnet is particularly desirable. Crystal size is crucial – specimens exceeding a millimeter in length are already considered exceptional. ## Popular localities The only source of collector specimens is the Dora-Maira Massif in Italy. Specimens from this locality are considered classic and most valuable.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft brush to remove dust. Given its occurrence as inclusions in harder minerals (like pyrope), washing in water is not recommended to avoid damaging the host rock. ## What to avoid Avoid contact with chemicals, especially strong acids and bases. Despite its relatively high hardness, protect it from impacts and contact with harder minerals to prevent scratches. Do not subject it to sudden temperature changes. ## Storage Collector specimens of phosphoellenbergerite, usually in the form of microscopic inclusions, are best stored in specialized "micromount" boxes, which protect against dust and mechanical damage. Exposure to strong sunlight is not advisable.

External references

https://www.mindat.org/min-7232.html