Hydroxylphosphohedyphane

Chemical formula: Ca<sub>2</sub>Pb<sub>3</sub>(PO<sub>4</sub>)<sub>3</sub>(OH)

Hydroxylphosphohedyphane is a rare mineral of the apatite group, being the hydroxyl analogue of phosphohedyphane, forming small, hexagonal crystals.

## Characteristics Hydroxylphosphohedyphane is a mineral belonging to the apatite supergroup. It occurs as small, hexagonal, prismatic or tabular crystals, rarely exceeding 1 mm in length. It also forms radial, rosette-like, or spherulitic aggregates. It is a brittle mineral. ## Physical Properties Crystals exhibit a hardness of approximately 4 on the Mohs scale. The luster is vitreous to resinous. The mineral is transparent to translucent. The density is approximately 5.85 g/cm³. ## Colors and Varieties Hydroxylphosphohedyphane is colorless, white, or has a pale yellow hue. No varieties have been distinguished. ## History and Name The mineral's name refers to its chemical composition – indicating the dominance of the hydroxyl (OH) and phosphate (PO₄) groups, as well as its structural similarity to hedyphane. It was described as a new mineral in 2022 by a research team (Kampf et al.) based on specimens from the Blue Bell Mine in California, USA. ## Applications Due to its rarity and small crystal size, hydroxylphosphohedyphane is solely of interest to collectors and scientists.

Properties

Mohs hardness
4
Luster
Resinous to vitreous
Streak
White
Density
5.85
Cleavage
Imperfect on {0001}
Fracture
Conchoidal to uneven
Transparency
Transparent to translucent
Crystal system
Hexagonal

Diagnostic features

## Identification Identifying hydroxylphosphohedyphane based on visual characteristics is very difficult due to the small size of the crystals. Its characteristic hexagonal habit, vitreous luster, and occurrence in paragenesis with other rare secondary minerals in the oxidation zones of lead deposits are distinctive. ## Distinguishing from Similar Minerals It can be confused with other minerals of the apatite group, such as mimetite, pyromorphite, hydroxymimetite, or phosphohedyphane. Definitive differentiation is almost exclusively possible using advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS/WDS). ## Crystal Forms It most often forms elongated, prismatic crystals with a hexagonal cross-section. It also occurs in the form of fibrous, radial aggregates and as spherical spherulites.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation zones of polymetallic hydrothermal deposits rich in lead and phosphorus. It forms as a result of the alteration of earlier ore minerals. ## Mineral Associations This mineral co-occurs with other secondary lead minerals, such as cerussite, phosphohedyphane, hydroxymimetite, mimetite, wulfenite, anglesite, as well as quartz and goethite. ## Localities The most important and best-documented localities from which reference specimens originate are: - Blue Bell Mine, San Bernardino County, California, USA (type locality). - Redmond Mine, Haywood County, North Carolina, USA.

Rarity

Very rare

For collectors

## Quality Criteria Specimens with well-formed, sharp crystals are most valued, even if they are small. Their grouping on a rock matrix and attractive association with other, color-contrasting minerals (e.g., orange wulfenite) are important. The clarity and transparency of the crystals also increase the specimen's value. ## Popular Localities Specimens from the type locality, the Blue Bell Mine in California, are most sought after by collectors specializing in rare or systematic minerals.

Care and storage

## Cleaning Great caution is advised. It is best to use compressed air to remove dust. If necessary, a soft brush can be used, avoiding strong pressure. Contact with water, especially tap water, is not recommended due to the risk of chemical reactions. ## What to Avoid Avoid all acids and strong bases, which can damage the mineral. It is sensitive to ultrasonic cleaners. Protect it from high temperatures and sudden temperature changes. ## Storage Specimens should be stored in stable conditions, in a closed display box, to protect them from dust and mechanical damage. Due to its lead content, hands should be washed after contact with the mineral.

Sources

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