Pengite

Chemical formula: (Pb₂+₈Sb₃+₃)Sb₅+₉O₃₅

Pengite is an extremely rare lead and antimony oxide, forming microscopic, tabular crystals with a metallic luster.

## Characteristics Pengite is a very rare mineral from the oxide group, composed of lead and antimony. It occurs as extremely small, tabular or bladed crystals, reaching sizes up to 0.1 x 0.05 x 0.01 mm. These crystals are usually flattened and elongated, often forming radial aggregates. Due to their microscopic size, its visual features are difficult to observe without specialized equipment. ## Physical Properties Pengite crystals exhibit a metallic luster and are opaque. Hardness and density have not been precisely measured due to the small size of the samples; however, the density calculated based on the chemical formula and unit cell parameters is 7.42 g/cm³. ## Colors and Varieties The mineral has a black color and a black streak. No varieties are known. ## History and Name Pengite was discovered in the Sb-Au-Pb-Zn mine in Xikuangshan, Hunan Province, China. It was approved as a new mineral species by the International Mineralogical Association (IMA) in 2017 (IMA2017-033). The name honors Peng Zhizhong (1914-2009), a Chinese crystallographer and mineralogist from the China University of Geosciences in Beijing, for his contributions to the mineralogy and crystallography of antimony ores.

Properties

Luster: Metallic
Streak: Black
Density: 7.42
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of pengite is possible only with advanced laboratory methods, such as X-ray diffraction (XRD) and chemical analysis using an electron microprobe (EDS/WDS). Recognition is impossible under collector or field conditions. Its characteristic feature is its occurrence as black, microscopic, tabular crystals in paragenesis with other antimony minerals. ## Distinguishing from Similar Minerals Pengite can be confused with other rare Sb-Pb oxides, such as clinocervantite, stibiconite, or bindheimite. Differentiation requires specialized analysis of chemical composition and crystal structure. ## Crystal Forms It forms very small, tabular or bladed crystals, flattened parallel to {010} and elongated along the [100] axis. Crystals often form small, radial aggregates.

Geological environment

## Genesis Pengite forms in the oxidation zones of hydrothermal deposits rich in antimony, lead, and gold. It occurs in cavities and fractures in siliceous rocks, which constitute the gangue of the deposit. ## Mineral Associations This mineral co-occurs with quartz, stibiconite, and clinocervantite. ## Localities The only confirmed locality of pengite in the world is its type locality - the Xikuangshan antimony, gold, lead, and zinc deposit in Lengshuijiang County, Loudi Prefecture, Hunan Province, China.

Rarity

Extremely rare

For collectors

## Quality Criteria As a mineral of purely scientific and micromount significance, the only criterion for evaluation is the confirmation of its identity by laboratory analysis and the abundance and quality of crystals within the microscope's field of view. These specimens are practically non-existent on the commercial market and are found mainly in research institutions.

Care and storage

## Cleaning Due to the extreme rarity and microscopic size of the crystals, pengite specimens should not be cleaned by any mechanical or chemical means. Any attempt at cleaning risks irreversible damage to the mineral. These specimens are of scientific value only and should be handled exclusively under laboratory conditions. ## What to Avoid Absolutely everything should be avoided: contact with chemicals, ultrasound, temperature changes, moisture, and even touch. The mineral is embedded in a rock matrix, and any interference can damage it. ## Storage Specimens should be stored exclusively in specialized, stable micromount containers that protect against dust, shocks, and changes in environmental conditions. Storage in a dry place is crucial.

Sources

IMA Mineral List (CNMNC)