Parasterryite

Chemical formula: Ag₁+₄Pb₂+₂₀(Sb₃+,As₃+)₂₄S₂-₅₈

Parasterryite is an extremely rare lead, silver, antimony, and arsenic sulfosalt, forming acicular crystals with a metallic luster.

## Characteristics Parasterryite is a complex sulfosalt from the lead sulfosalt group, classified as a polymorph of sterryite. It forms microscopic, acicular or fibrous crystals with a metallic luster and black color. These crystals are flexible and typically occur as tangled or partially ordered aggregates on a rock matrix. Due to its microscopic nature, it is a mineral primarily of interest to scientists and specialized collectors. ## Physical Properties This mineral is characterized by a strong metallic luster and is completely opaque. Its density, calculated based on its chemical composition and unit cell parameters, is 5.95 g/cm³. The Mohs hardness has not yet been determined. ## Colors and Varieties Parasterryite occurs exclusively in black. No colored or commercial varieties are known. ## History and Name The mineral's name refers to its close relationship with sterryite, with the prefix "para-" indicating polymorphism or structural similarity. It was first described in 2014 by a team of mineralogists led by Cristian Biagioni. The type locality and only known occurrence is the Pollone mine in Valdicastello Carducci, Tuscany, Italy. ## Uses Parasterryite has no commercial or industrial applications. Its significance is purely scientific and for collectors.

Properties

Luster: Metallic
Streak: Black
Density: 5.95
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Amateur identification of parasterryite is practically impossible. Its characteristic feature is its occurrence as black, metallically lustrous, tangled aggregates of acicular or fibrous crystals. A key indicator is the specimen's origin from the only known locality – the Pollone mine in Italy. ## Differentiation from Similar Minerals Parasterryite is visually indistinguishable from many other acicular sulfosalts, particularly sterryite, with which it co-occurs. It can also be confused with other lead and antimony sulfosalts. Definitive differentiation requires advanced analytical techniques, such as X-ray diffraction (XRD) or energy-dispersive X-ray spectroscopy (EDS). ## Crystal Forms This mineral forms elongated, acicular to fibrous crystals that are flexible. These crystals rarely occur individually, most often forming dense, tangled, or radial aggregates.

Geological environment

## Genesis Parasterryite forms as a result of low-temperature hydrothermal processes. It occurs in barite-pyrite veins, cutting through an iron oxide deposit located within a metamorphic complex consisting of phyllites and quartzites. ## Mineral Associations This mineral occurs in direct association with sterryite, sphalerite, pyrite, and barite. ## Localities The only confirmed locality of parasterryite in the world is its type locality – the Pollone mine, located in Valdicastello Carducci, in the province of Lucca, Tuscany, Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria For microscopic minerals such as parasterryite, the collector's value of a specimen is determined by the richness and abundance of the mineral on the rock matrix. Samples with dense, well-formed aggregates of fibrous crystals are most highly valued. The presence of other rare associated minerals, especially sterryite, is an additional asset. ## Popular Localities The only source of parasterryite specimens is the Pollone mine in Italy. All samples available on the collector's market originate from this single locality.

Care and storage

## Cleaning Parasterryite specimens are extremely delicate and consist of microscopic, fibrous crystals. Mechanical cleaning, including with brushes, should be avoided. The safest method for dust removal is to use compressed air from a safe distance. Do not use water or any chemical agents. ## What to Avoid As a sulfosalt, parasterryite can be sensitive to chemicals, acids, and bases. Ultrasonic cleaners, which could damage delicate crystal aggregates, should be avoided. The mineral should be protected from high temperatures and humidity. ## Storage It is recommended to store specimens in enclosed "micromount" containers, which protect them from dust, mechanical damage, and sudden changes in environmental conditions. This is the best way to secure fragile and small crystals.

Sources

IMA Mineral List (CNMNC)