Symesite

Chemical formula: Pb<sup>2+</sup><sub>10</sub>S<sup>6+</sup>O<sub>4</sub>O<sub>7</sub>Cl<sub>4</sub>·H<sub>2</sub>O

Symesite is a very rare, secondary lead mineral with a characteristic canary-yellow color, occurring as tabular crystals.

## Characteristics Symesite is a complex hydrated lead sulfate-oxychloride. It forms characteristic, small aggregates composed of thin, tabular or platy crystals. Its most recognizable feature is its intense, canary-yellow to orange-yellow color. Crystals rarely occur individually, most often forming fan-shaped or nearly parallel intergrowths, densely covering the surface of the host rock. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 4. It exhibits an adamantine to resinous luster and a high density of approximately 6.56 g/cm³, which is typical for lead minerals. It is translucent and shows perfect cleavage in one plane, which accounts for its platy appearance. ## Colors and Varieties Symesite occurs in uniform, bright shades of yellow, from canary to orange-yellow. No color or commercial varieties are distinguished. ## History and Name The mineral was described in 1998. Its name honors Robert Frederick Symes (born 1939), a British mineralogist and curator at the Natural History Museum in London, in recognition of his contributions to the study of secondary minerals from the Mendip Hills in England, where symesite was discovered. The type locality is Merehead Quarry in Somerset. ## Uses Due to its extreme rarity and small crystal size, symesite has no industrial applications. It is solely an object of scientific and collecting interest.

Properties

Mohs hardness
4
Luster
Adamantine to Resinous
Streak
Pale yellow
Density
6.56
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Translucent
Crystal system
Triclinic

Diagnostic features

## Identification Key diagnostic features of symesite include its canary-yellow color, platy crystal habit, adamantine luster, high density, and specific occurrence environment. Reaction with acids is not recommended as an identification method. ## Distinguishing from Similar Minerals Symesite is sometimes confused with other yellow, secondary lead minerals. It is distinguished from wulfenite by its crystal habit (tabular, not square) and crystallographic system (triclinic, not tetragonal). It differs from mimetite by its habit (platy, not prismatic) and luster (more adamantine than resinous). Final identification is often possible through analysis of the mineral association and locality. ## Crystal Forms Symesite forms thin, tabular crystals with a hexagonal outline, which almost always occur as aggregates. These aggregates take on rosette, fan-shaped, or subparallel intergrowth forms.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation zone of lead and manganese ore deposits, which occur in carbonate rocks (limestones). It forms under low-temperature conditions as a result of the alteration of primary ore minerals. ## Mineral Associations Symesite often co-occurs with other rare, secondary lead minerals, such as mendipite, chloroxiphite, diaboleite, paralaurionite, as well as with more common cerussite and hydrocerussite. The presence of these minerals is a strong diagnostic indicator. ## Localities The most important and historically first occurrence is Merehead Quarry (Torr Works) in Cranmore, Somerset, England. It is also known from the Finch Mine in Gila County, Arizona, USA. These are the only confirmed, significant localities for this mineral worldwide.

Rarity

Very rare

For collectors

## Quality Criteria The most highly prized symesite specimens are characterized by rich coverage of the substrate by bright yellow, well-formed crystal aggregates. A contrasting, dark rock matrix enhances visual appeal. Samples where symesite co-occurs with other rare minerals from the same locality, such as purple mendipite or green chloroxiphite, are of exceptional value. ## Popular Localities The vast majority of the best collector specimens come from the type locality – Merehead Quarry in England. This is the classic locality for this mineral, and specimens from there are a benchmark of quality.

Care and storage

## Cleaning Symesite specimens should only be dry-cleaned, using a soft brush or a stream of compressed air to remove dust. Avoid contact with water and any chemical agents. ## What to Avoid The mineral is sensitive to moisture and chemicals, especially acids. Ultrasonic cleaners must not be used. As a lead mineral, it is toxic if ingested or if dust is inhaled – wash hands after handling the specimen. ## Storage It is recommended to store specimens in a dry, stable environment, preferably in a sealed "micromount" box, which protects against dust, moisture, and mechanical damage.

Sources

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