Rumseyite
Chemical formula: Pb<sup>2+</sup><sub>2</sub>OFCl
Rumseyite is a rare mineral from the lead halide group, forming tiny, hexagonal crystals with a pearly luster.
Properties
- Mohs hardness
- 2
- Luster
- Pearly, Vitreous
- Streak
- White
- Density
- 7.35
- Cleavage
- Perfect on {0001}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Hexagonal
Diagnostic features
## Identification Identification of rumseyite is primarily based on its characteristic crystal habit – small, hexagonal, tabular crystals, often in rosette-like aggregates. Pearly luster, high density (perceptible even in small fragments), and co-occurrence with other rare lead halides in a specific geological environment are key indicators. Final confirmation requires advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Rumseyite can be confused with other colorless, secondary lead minerals with a tabular habit, such as mendipite or cerussite. It is distinguished by its hexagonal crystal shape (mendipite is orthorhombic) and flexibility. Compared to cerussite, rumseyite has a lower luster and a different crystal form. ## Crystal Forms It forms thin, tabular crystals with a hexagonal outline. These crystals often arrange themselves into fan-shaped, rosette-like, or almost spherical aggregates.
Geological environment
## Genesis Rumseyite is a secondary mineral, formed in the oxidation zones of polymetallic deposits, under specific low-temperature conditions. Its formation is associated with the interaction of chlorine-rich solutions with primary lead minerals in the presence of oxygen. It occurs in cavities and fissures of manganese rocks. ## Mineral Associations This mineral co-occurs with other rare, secondary lead minerals, such as mendipite, diaboleite, parkinsonite, symesite, mereheadite, and cerussite. ## Localities The most important and type locality for rumseyite is the Torr Works quarry (Merehead Quarry) in Cranmore, Somerset, England. It has also been identified in several other localities worldwide, including the mines of the Laurion district in Greece and the Wesley mine in the Flinders Ranges region of South Australia.
Rarity
Very rare
For collectors
## Quality Criteria For rumseyite collectors, the quality and definition of the crystals are paramount. Specimens with sharp, well-formed, hexagonal crystals forming aesthetic, rosette-like aggregates are most valued. Contrast with the rock matrix and the presence of rare associated minerals are also important. Crystal size, though usually microscopic, also affects value – larger, well-formed tablets are rare. ## Popular Localities By far the most sought-after and classic specimens come from the type locality – the Torr Works quarry in Somerset, England. Material from this location is considered exemplary for the species.
Care and storage
## Cleaning Rumseyite specimens, typically micromounts, do not require cleaning. If absolutely necessary, compressed air (from a safe distance) can be used to remove dust. Avoid contact with water and any chemicals. ## What to Avoid Absolutely avoid contact with acids and other chemicals, which can destroy the mineral. The crystals are very small, soft, and delicate, so they should be protected from any impact or abrasion. Due to its lead content, avoid inhaling dust and wash hands after contact with the mineral. ## Storage The best storage method is to place the specimen in a micromount box, which protects it from dust, mechanical damage, and direct contact.