Fiedlerite
Chemical formula: Pb<sup>2+</sup><sub>3</sub>Cl<sub>4</sub>F(OH)·H<sub>2</sub>O
Fiedlerite is a rare, secondary lead halide, found in the oxidation zones of lead deposits and in ancient, seawater-exposed metallurgical slags.
Properties
- Mohs hardness
- 3.5
- Luster
- Vitreous, Pearly
- Streak
- White
- Density
- 5.88
- Cleavage
- Perfect on {001}
- Fracture
- Conchoidal
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Fiedlerite can be identified by its tabular or prismatic crystal habit, high density (the specimen feels heavy for its size), vitreous luster, and perfect cleavage. Its occurrence in paragenesis with other secondary lead minerals in ancient slags or oxidation zones is also characteristic. ## Distinguishing from Similar Minerals It can be confused with other colorless lead halides, such as laurionite or paralaurionite, with which it often co-occurs. Differentiation requires precise crystallographic studies (angles between faces) or analytical methods such as X-ray diffraction (XRD). It differs from anglesite and cerussite by a lower refractive index and lack of reaction with acids (cerussite effervesces). ## Crystal Forms Fiedlerite crystals are typically flattened, tabular, elongated, or prismatic. They often form twins, including multiple twins, creating fan-shaped, radial, or reticulated aggregates.
Geological environment
## Genesis Fiedlerite is a secondary mineral. It forms as a result of the reaction of lead-rich, ancient metallurgical slags with seawater. It also occurs, though less frequently, as a product of the oxidation of lead ore deposits (mainly galena) in the presence of chloride-rich solutions, under low temperature and pressure conditions. ## Mineral Associations It most commonly co-occurs with other secondary lead halides, such as laurionite, paralaurionite, penfieldite, and phosgenite. It also occurs in association with cerussite and anglesite. ## Localities The most important and classic locality for fiedlerite is the ancient slag heaps in the Laurion region of Attica (Greece). It has also been found in slag deposits in Baratti (Tuscany, Italy) and in the Grand Reef Mine in Graham County (Arizona, USA).
Rarity
Very rare
For collectors
## Quality Criteria The most prized fiedlerite specimens are those with well-formed, sharp, and transparent crystals, forming aesthetic groups or fan-shaped aggregates. The absence of mechanical damage and attractive contrast with the rock matrix or other associated minerals, e.g., intensely colored cerussite, is important. Crystal size is also crucial, as large, well-formed specimens are exceptionally rare. ## Popular Localities Specimens from the classic locality in Laurion, Greece, are by far the most sought after by collectors. Material from this location is the historical standard for the species and has yielded the best known crystals.
Care and storage
## Cleaning Fiedlerite specimens should be cleaned with the utmost care, using only a soft brush to remove dust. Contact with water, especially demineralized water, can lead to its slow dissolution or chemical degradation. Ultrasonic cleaners should be avoided. ## What to Avoid The mineral is sensitive to chemicals, including acids and bases. Sudden temperature changes and prolonged exposure to strong light, which can affect its properties, should be avoided. Due to its lead content, inhalation of dust should be avoided, and hands should be washed after contact with the specimen. ## Storage Fiedlerite should be stored under stable conditions, preferably in a closed, padded box or display case, to protect it from mechanical damage and dust. It should be kept away from minerals that could scratch it.