Mélonjosephite

Chemical formula: CaFe²⁺Fe³⁺(PO₄)₂(OH)

Mélonjosephite is a rare calcium iron hydroxyl phosphate, forming dark green, almost black, transparent crystals.

## Characteristics Mélonjosephite is a complex calcium and iron phosphate, belonging to the group of rare minerals. It forms tabular or bladed crystals, often grouped into radial aggregates. Its most characteristic feature is its very dark green color, which in many cases appears almost black. Specimens are usually small, and well-formed crystals are rare. ## Physical Properties This mineral has a hardness of 5 on the Mohs scale. It is relatively dense, with a specific gravity of 3.65 g/cm³. The crystals are transparent, which is especially visible in thin fragments where their green color is revealed. The luster is vitreous. ## Colors and Varieties The dominant and only recorded color of mélonjosephite is dark green, often so intense that it appears black. No named color or commercial varieties are distinguished. ## History and Name The mineral's name honors Mélon Joseph (1903-1977), a Belgian mineralogist and crystallographer from the University of Ghent, who made significant contributions to phosphate research. The mineral was described and approved as a new species in 1976. ## Uses Mélonjosephite has no industrial application. Its significance is purely scientific and as a collector's item, as a rare and well-defined mineralogical species.

Properties

Mohs hardness: 5
Luster: Vitreous
Streak: Greenish
Density: 3.65
Cleavage: One, longitudinal; another, transverse
Fracture: Uneven
Transparency: Transparent
Crystal system: Orthorhombic

Diagnostic features

## Identification Key diagnostic features include a very dark green, almost black color, tabular or bladed crystal habit, often in radial aggregates, and a greenish streak. Occurrence in granitic pegmatites in association with other phosphates is also an important clue. ## Distinguishing from Similar Minerals It can be confused with other dark phosphate minerals such as strengite, rockbridgeite, or dufrenite. Differentiation often requires chemical or crystallographic analysis. Mélonjosephite is distinguished by its specific chemical composition (presence of calcium and iron in two oxidation states) and a characteristic greenish streak. ## Crystal Forms It crystallizes in the orthorhombic system. It most often forms thin, tabular or bladed crystals, which can combine into fan-shaped or radial aggregates. Single, well-formed crystals are less common.

Geological environment

## Genesis Mélonjosephite is a hydrothermal mineral, crystallizing in the late stages of granitic pegmatite evolution. It forms as a result of the alteration of primary phosphates, such as triphylite, under calcium-enriched conditions. ## Mineral Associations This mineral coexists with other phosphates typical of pegmatites. It is most often found in association with quartz, albite, muscovite, strengite, rockbridgeite, dufrenite, beryl, and iron and manganese oxides. ## Localities The most important and also the type locality (localitas typica) is the Angarf-South pegmatite in the Ouarzazate Province, Dara-Tafilalt region, Morocco. This is the only locality from which well-characterized specimens of this mineral originate.

Rarity

Very rare

For collectors

## Quality Criteria The most highly valued mélonjosephite specimens are those with sharp, well-formed crystals exhibiting a distinct, though dark, green color and luster. Radial aggregates of crystals embedded in a contrasting matrix, such as white quartz or albite, are particularly sought after. The size of the crystals and the entire specimen also significantly influence its value. ## Popular Localities The only source of collector specimens is the Angarf-South pegmatite in Morocco. Specimens from this locality are considered exemplary for this species.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. After wet cleaning, the specimen should be thoroughly dried. ## What to Avoid Avoid contact with acids and other aggressive chemicals that can damage the mineral's surface. It should not be heated or subjected to ultrasound. Due to its possible sensitivity to chemical changes, it should be protected from moisture. ## Storage Collections containing mélonjosephite should be stored under stable conditions, in a dry place, away from direct sunlight. It is best to place it in a separate, padded display box to avoid scratches from harder minerals.

External references

https://www.mindat.org/min-2640.html