Haywoodite
Chemical formula: [Pb²⁺(H₂O)₁₀][Zn²⁺₁₂(OH)₂₀(H₂O)(S⁶⁺O₄)₃]
Haywoodite is an extremely rare, hydrated zinc and lead sulfate, forming colorless, hexagonal tabular crystals.
Properties
- Mohs hardness
- 2.5-0
- Color
- Colorless to pale pink
- Luster
- Vitreous
- Streak
- White
- Density
- 3.27
- Cleavage
- on {011}
- Fracture
- Step-Like
- Transparency
- Transparent
- Crystal system
- Triclinic
Diagnostic features
## Identification Identifying Haywoodite in the field is practically impossible due to the microscopic size of the crystals. Identification requires advanced laboratory techniques, such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS). In a collection, it can be identified based on the label and confirmed locality. The characteristic habit is small, colorless, hexagonal tabular crystals. ## Distinguishing from Similar Minerals Haywoodite can be confused with other secondary, colorless sulfates found in the oxidation zones of zinc and lead deposits, such as namuwite or ramsbeckite. Distinguishing it from these is only possible using X-ray diffraction (XRD), which reveals Haywoodite's unique crystal structure. ## Crystal Forms The mineral forms thin, tabular crystals with a hexagonal outline, often grouped into small aggregates or rosettes on the surface of the host rock.
Geological environment
## Genesis Haywoodite is a secondary mineral, formed in the oxidation zones of zinc and lead deposits. It forms as a result of the weathering of primary ore minerals, such as sphalerite and galena, in the presence of sulfate-rich waters. It crystallizes under low-temperature conditions, filling voids and fractures in rocks. ## Mineral Associations This mineral co-occurs with other secondary zinc and lead minerals. At its type locality (Torr Works quarry), it was found in association with namuwite, gypsum, hydrocerussite, and calcite. ## Localities The only confirmed occurrence of Haywoodite worldwide is its type locality: Torr Works quarry (also known as Merehead Quarry) in Cranmore, Somerset, England.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of a Haywoodite specimen primarily depends on the presence of well-formed, sharp, and as large as possible crystals. Since the crystals are microscopic, their abundance on the rock matrix and aesthetic arrangement are crucial. Contrast with the substrate and the presence of rare associated minerals also increase its collector's value. The most valuable specimens are those co-occurring with other rare minerals from this locality. ## Popular Localities The only source of Haywoodite specimens is the Torr Works quarry in Somerset, England. Material from this locality is highly sought after by collectors specializing in systematic minerals and "micromount" specimens.
Care and storage
## Cleaning Haywoodite specimens are extremely delicate and small, therefore they should not be cleaned mechanically. Any attempts to use brushes, even soft ones, can damage the microscopic crystals. If cleaning is absolutely necessary, the specimen can be carefully rinsed in distilled water and then allowed to air dry completely without heating. ## What to Avoid Avoid contact with any chemicals, including acids and detergents. The mineral is very soft (hardness 2), so it is susceptible to scratches and mechanical damage. It should be protected from high temperatures and sudden temperature changes. Due to its hydrated structure, storage in a very dry environment can potentially lead to dehydration. ## Storage Specimens should be stored under stable conditions, in enclosed "micromount" containers, to protect them from dust, physical damage, and humidity changes. It is best to keep them away from direct sunlight and heat sources.