Dongchuanite

Chemical formula: Pb₂+₄Zn₂+Zn₂+₂(PO₄)₄(OH)₂

Dongchuanite is a very rare phosphate mineral, discovered in China, forming aggregates of small, platy, white crystals.

## Characteristics Dongchuanite is a hydrated zinc lead phosphate belonging to the jamesite group. It occurs as aggregates and rosettes composed of very small, thin, platy crystals, reaching sizes up to 200 μm in length, 50 μm in width, and merely 5 μm in thickness. Individual crystals are colorless, but in aggregates, they form white, chalky coatings and masses. ## Physical Properties Dongchuanite crystals exhibit a white color and a white streak. They have a pearly luster on cleavage surfaces and a vitreous luster on other faces. The mineral is transparent to translucent. Due to its small size and mode of occurrence, precise determination of hardness and density was not possible. The density calculated based on the chemical formula and unit cell parameters is 5.63 g/cm³. ## History and Name The mineral's name comes from its discovery locality – the Dongchuan copper mine in Yunnan Province, China. It was approved by the International Mineralogical Association (IMA) in 2018 under the number IMA2018-016. It was described by a team of mineralogists, including Guowu Li, who is the author of many new minerals from this region. ## Uses Dongchuanite, as an extremely rare mineral occurring in microscopic crystals, has no industrial applications. Its significance is purely scientific and for collectors, being a coveted object for specialized collectors of rare minerals (so-called "micromounts").

Properties

Luster: Pearly
Streak: White
Density: 5.63
Cleavage: Perfect on {100}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Triclinic

Diagnostic features

## Identification Identification of dongchuanite with the naked eye is impossible. Identification requires advanced analytical techniques, such as Raman spectroscopy and electron microprobe chemical analysis (EDS/WDS) to confirm its composition (presence of lead, zinc, and phosphorus). Visually, under high magnification, characteristic aggregates of small, white, platy crystals can be observed. ## Distinguishing from Similar Minerals Dongchuanite can be confused with other secondary, white zinc and lead minerals, such as hydrocerussite, sphalerite, or smithsonite in the form of coatings. Definitive differentiation is only possible through chemical and crystallographic analysis. Its unique structure within the jamesite group is a key diagnostic feature at the research level. ## Crystal Forms Crystals are very thin, platy, lath-like, elongated along one of the axes. They form rosette-like or randomly oriented aggregates on the surface of the host rock.

Geological environment

## Genesis Dongchuanite is a secondary mineral that forms in the oxidation (weathering) zones of polymetallic deposits. It results from the alteration of primary ore minerals containing zinc and lead, in the presence of phosphate-rich solutions. ## Mineral Associations At the type locality (Dongchuan mine), dongchuanite coexists with minerals such as quartz, pyromorphite, anglesite, cerussite, as well as newly discovered minerals from this locality, like liuleite and dongchuanite. ## Localities The only confirmed locality for dongchuanite in the world is its type locality – the Dongchuan copper mine, Dongchuan District, Kunming, Yunnan Province, China. This is one of the most important sites for the discovery of new, rare secondary minerals.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of dongchuanite specimens is primarily assessed based on the richness and aesthetics of the microcrystal aggregates. Most valued are specimens with clearly formed, white rosettes or dense crystalline clusters, contrasting with the color of the host rock (matrix). Due to the microscopic size of the crystals, clarity and transparency are not key criteria in visual assessment. ## Popular Localities The only source of dongchuanite specimens is the Dongchuan mine in China. Specimens from this locality are highly sought after by collectors specializing in mineral systematics and in so-called "micromounts."

Care and storage

## Cleaning Dongchuanite specimens are extremely delicate and consist of microscopic crystals. They should not be cleaned mechanically or chemically. Any attempts at cleaning, even with compressed air, can irreversibly destroy the specimen. It is best to leave it in its untouched state. ## What to Avoid Avoid contact with water, acids, bases, and any solvents. The mineral is sensitive to vibrations and impacts. It should not be touched, as the brittle crystals may crumble. ## Storage Specimens should be stored exclusively in specialized micromount boxes, which protect them from dust, humidity, and mechanical damage. Store in stable conditions, away from sources of vibration and sudden temperature changes.

Sources

IMA Mineral List (CNMNC)