Parkinsonite
Chemical formula: Pb<sup>2+</sup><sub>7</sub>Mo<sup>6+</sup>O<sub>9</sub>Cl<sub>2</sub>
Parkinsonite is a very rare lead molybdate chloride, forming tiny, tabular crystals of an intense yellow color.
Description
## Characteristics Parkinsonite is a mineral from the molybdate group, valued for its intense, bright yellow or orange-yellow color. It occurs as very small, thin, square, tabular crystals. These crystals rarely exceed 1 mm and often form subparallel or rosette aggregates on the surface of the host rock. It exhibits a strong luster, described as adamantine or resinous, which, combined with its vivid color, gives it an attractive appearance despite its small size. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of approximately 3. It is also very dense, with a density calculated from its chemical composition and crystal structure of 7.55 g/cm³. It is translucent and does not exhibit cleavage, and its fracture is conchoidal. ## Colors and Varieties Parkinsonite occurs in uniform, saturated colors ranging from bright yellow to orange-yellow. No color varieties or commercial varieties are known. ## History and Name The mineral's name honors British mineral collector Eric Parkinson (born 1928), who found the first specimens. Parkinsonite was described as a new mineral species in 1994 by M.D. Welch, A.J. Criddle, and A.M. Clark based on material from the Merehead Quarry in England. ## Uses Due to its extreme rarity and small crystal size, parkinsonite has no industrial applications. It is of scientific and collectible significance only, being a desirable acquisition for specialized collections of rare minerals and microminerals.
Diagnostic features
## Identification Characteristic features of parkinsonite include its bright yellow color, strong adamantine luster, and the form of thin, square, tabular crystals. The location and co-occurrence with other rare secondary lead minerals, such as mendipite, are also crucial for identification. ## Distinguishing from Similar Minerals Parkinsonite is sometimes confused with wulfenite, which also forms yellow or orange tabular crystals. However, wulfenite usually has larger crystals, a slightly different hue, and crystallizes in the tetragonal system with different symmetry. It is distinguished from mimetite by its crystal form – mimetite most often forms hexagonal, prismatic, or barrel-shaped crystals. ## Crystal Forms Parkinsonite forms thin, tabular crystals with a square outline, dominated by the {001} face. They occur singly or in small, partially overlapping groups and fan-shaped aggregates.
Geological environment
## Genesis Parkinsonite is a secondary mineral formed in the oxidation zones of polymetallic deposits, under specific geochemical conditions. At the type locality (Merehead Quarry), it occurs in voids within manganese nodules deposited in hydrothermally altered limestones. ## Mineral Associations This mineral co-occurs with other rare, secondary lead minerals, such as mendipite, blixite, hydrocerussite, cerussite, and also with calcite. ## Localities The most important and well-known locality for parkinsonite is its type locality – Merehead Quarry (Torr Works) in Cranmore, Somerset, England. This is the site from which the vast majority of the best specimens in the world originate. It has also been reported in trace amounts in Långban, Sweden.
Rarity
Very rare
Collector aspects
## Quality Criteria The most highly prized parkinsonite specimens are those characterized by an abundance of well-formed, sharp microcrystals with an intense, saturated color. Crystal size is also important – although always small, specimens with crystals approaching 1 mm are exceptionally desirable. Aesthetic arrangement on a small rock matrix and association with other rare minerals, e.g., purple mendipite, significantly increase the collectible value of the specimen. ## Popular Localities The only commercially significant source of collectible parkinsonite specimens is the Merehead Quarry in Somerset, England. Specimens from this locality are considered the world standard for this mineral.
Care and storage
## Cleaning Parkinsonite specimens should be cleaned with the utmost care, preferably using a soft brush or a stream of compressed air to remove dust. The crystals are extremely small and fragile. Ultrasonic cleaners and aggressive mechanical methods should be avoided. ## What to Avoid The mineral is soft and susceptible to scratching. It should be protected from contact with harder minerals. As a chloride, it may react with some acids, so all chemicals should be avoided. ## Storage The safest way to store parkinsonite is to place it in a specialized micromount box. This protects the delicate crystals from mechanical damage, dust, and contact with other specimens.