Phosphohedyphane

Chemical formula: Ca<sub>2</sub>Pb<sup>2+</sup><sub>3</sub>(PO<sub>4</sub>)<sub>3</sub>Cl

Phosphohedyphane is a rare mineral from the apatite group, a phosphate analog of hedyphane, valued for its well-formed, hexagonal crystals.

## Characteristics Phosphohedyphane is a mineral belonging to the apatite group and is the phosphate analogue of hedyphane. It typically forms well-developed, hexagonal crystals with prismatic or tabular habits, often terminated by pyramids. Crystals can be colorless, white, gray, and sometimes take on pale yellow or greenish hues. It occurs as single crystals or in radial aggregates and granular masses. ## Physical Properties This mineral is characterized by a hardness of approximately 4.5 on the Mohs scale. Its luster is most often vitreous to resinous. It is a relatively heavy mineral due to its lead content, and its density is about 5.87 g/cm³. It is transparent to translucent. ## Colors and Varieties Phosphohedyphane is usually colorless to white. Specimens with gray, pale yellow, and more rarely greenish colors are also found. No distinct varieties of this mineral are recognized. ## History and Name The mineral's name refers to its chemical composition (phosphate) and its structural relationship with hedyphane. It was formally described and recognized by the International Mineralogical Association (IMA) in 2004. The type locality (locus typicus) is the "Kombat" mine in Namibia. ## Uses Phosphohedyphane has no industrial applications. Due to its rarity and attractive crystals, it is a sought-after and valued collector's mineral.

Properties

Mohs hardness
4.5
Luster
Vitreous to resinous
Streak
White
Density
5.87
Cleavage
Indistinct on {0001} and {1010}
Fracture
Conchoidal to uneven
Transparency
Transparent to translucent
Crystal system
Hexagonal

Diagnostic features

## Identification Key diagnostic features of phosphohedyphane include its hexagonal, prismatic or tabular crystals, high density (perceptible weight in hand), vitreous-resinous luster, and relatively low hardness. It reacts with nitric acid. ## Distinguishing from Similar Minerals Phosphohedyphane can be confused with other minerals from the apatite group, such as mimetite, pyromorphite, or vanadinite. It is distinguished from mimetite and pyromorphite by the presence of calcium and chlorine in its composition, which requires advanced chemical analysis (EDS/WDS). Visually, it may be indistinguishable from colorless or white varieties of these minerals. Compared to vanadinite, it usually has less intense colors. ## Crystal Forms It most often forms hexagonal, prismatic crystals, often short and tabular. Crystals are sometimes terminated by flat pinacoids or hexagonal pyramid faces. It also occurs as radial aggregates or granular masses.

Geological environment

## Genesis Phosphohedyphane is a secondary mineral, formed in the oxidation (weathering) zones of lead and copper ore deposits. It forms as a result of the alteration of primary lead minerals in a phosphate-rich environment. ## Mineral Associations This mineral often co-occurs with other secondary lead minerals. At the type locality (Kombat mine), it was found in association with duftite, mimetite, quartz, calcite, and hematite. ## Localities The most important and typical occurrence of phosphohedyphane is the Kombat mine, in the Otjozondjupa Region, Namibia, from which the best-known specimens originate. Other confirmed localities include the "Glücksstern" mine in North Rhine-Westphalia, Germany, and the "Adelaide" mine in Nevada, USA.

Rarity

Rare

For collectors

## Quality Criteria The most desired specimens by collectors are those with well-formed, sharp, and lustrous crystals of high transparency. Crystals with a distinct, hexagonal outline, especially those with a tabular habit, are highly prized. Contrasting placement on a rock matrix, for example with dark hematite or duftite, significantly enhances the value and aesthetics of the specimen. Crystal size and their abundance on the matrix are also key factors. ## Popular Localities Undoubtedly, the most valued and sought-after specimens come from the type locality – the Kombat mine in Namibia. Specimens from this locality have set the standard of quality for this mineral.

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. Ensure the specimen is completely dry before storage. ## What to Avoid As a lead-containing mineral, it is toxic if ingested or if dust is inhaled – always wash hands after contact. Avoid contact with acids and other aggressive chemicals. It is relatively soft, so it must be protected from scratching by harder minerals. It should not be heated or exposed to sudden temperature changes. ## Storage Phosphohedyphane specimens should be stored in separate, padded boxes or display cases to prevent scratches and mechanical damage. They should be protected from dust and moisture. Due to lead toxicity, it should be stored out of reach of children and pets.

Sources

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