Hydroxylmattheddleite

Chemical formula: Pb₁₀(SiO₄)₃(SO₄)₃(OH)₂

Hydroxylmatteddleite is a very rare, secondary lead silicate-sulfate, forming colorless, hexagonal crystals with an adamantine luster.

## Characteristics Hydroxylmatteddleite is a mineral from the silicate and sulfate group, being a hydroxyl analog of matteddleite. It most often forms well-developed, hexagonal, prismatic or acicular crystals. It also occurs in radial or fan-shaped aggregates. Crystals are usually small, making it a typical micromount mineral. A characteristic feature is a very strong, adamantine luster on the crystal faces. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 3-4. It is transparent to translucent. Due to its high lead content, it has a high density of approximately 6.66 g/cm³. The luster is adamantine, and the streak is white. ## Colors and Varieties Hydroxylmatteddleite is usually colorless or white. No colored varieties or trade names are distinguished. ## History and Name The mineral was formally described and recognized by the IMA in 2000. Its name refers to its close relationship with matteddleite, indicating the dominance of hydroxyl (OH) groups in its structure where matteddleite contains chlorine. Mattheddleite, in turn, was named after the Scottish mineralogist Matthew Forster Heddle (1828-1897). ## Uses Due to its rarity and small crystal size, hydroxylmatteddleite has no industrial application. It is solely an object of scientific and collecting interest.

Properties

Mohs hardness: 3-4
Luster: Adamantine
Streak: White
Density: ok. 6.66 (obliczona)
Cleavage: Good on {0001} and {10-10}
Fracture: Conchoidal to Uneven
Transparency: Transparent to Translucent
Crystal system: Hexagonal

Diagnostic features

## Identification Key diagnostic features include the hexagonal crystal habit, very strong adamantine luster, high density (the specimen is heavy for its size), and occurrence in paragenesis with other secondary lead minerals. Identification is most reliable based on chemical analysis. ## Distinguishing from Similar Minerals It can only be distinguished from matteddleite using advanced analytical methods (EDS, WDS) that allow for chemical composition determination. It differs from cerussite in crystal habit (cerussite often forms reticulated twins) and lack of reaction with hydrochloric acid. Leadhillite and susannite, although similar, crystallize in different systems and often have a tabular habit. ## Crystal Forms Crystals have a prismatic habit, often elongated (columnar) or acicular. Crystal terminations can be flat or pyramidal. They often form radial aggregates growing from a common substrate.

Geological environment

## Genesis Hydroxylmatteddleite is a secondary mineral, forming in the oxidation zones of lead deposits. It forms as a result of surface water action on primary ore minerals. It is a "post-mining" formation mineral, meaning it often crystallizes on old mine dumps or even on museum specimens due to slow reaction with air pollutants. ## Mineral Associations It co-occurs with other rare, secondary lead minerals such as matteddleite, leadhillite, susannite, cerussite, lanarkite, scotlandite, and macphersonite. ## Localities The most important and classic localities for this mineral are in the United Kingdom. The type locality is Leadhills in South Lanarkshire, Scotland. Another known occurrence is in the deposits of the Caldbeck Fells area in Cumbria, England.

Rarity

Very rare

For collectors

## Quality Criteria The most highly valued specimens are those with sharp, well-formed, transparent crystals with a strong luster. The richness and aesthetics of associations with other rare minerals are also of great importance. Due to the microscopic size of the crystals, their perfect form and lack of damage are crucial. ## Popular Localities The most sought-after specimens by collectors come from the classic localities in the United Kingdom: Leadhills in Scotland and Caldbeck Fells in England. Specimens from these locations are considered the global standard for this mineral.

Care and storage

## Cleaning Specimens should only be dry cleaned, using a soft brush or compressed air from a safe distance. The crystals are very brittle and delicate. Contact with water, especially with acids or detergents, is not recommended and can lead to damage to the crystal surfaces. ## What to Avoid Avoid ultrasonic cleaners, all chemicals, and sudden temperature changes. The mineral is soft and susceptible to scratching. As a lead mineral, it is toxic – hands should be washed after each contact with the specimen, and dust inhalation should be avoided. ## Storage It is recommended to store specimens in stable conditions, away from dust and moisture. The best solution is sealed micromount boxes, which protect delicate crystals from mechanical damage.

Sources

IMA Mineral List (CNMNC)