Dulanggouite

Chemical formula: Bi<sub>6</sub>Te<sub>3</sub>

Dulangouite is an extremely rare gold telluride, forming microscopic, anhedral grains with a metallic luster.

## Characteristics Dulangouite is a mineral from the telluride group, chemically gold telluride (AuTe₂). It occurs as very small, irregular (anhedral) grains, rarely exceeding 100 micrometers in size. It is opaque, with a creamy-white or grayish-white color and a characteristic metallic luster. It often forms intergrowths with other tellurides, such as calaverite, and with native gold. ## Physical Properties The mineral's luster is strongly metallic. Hardness has not been measured due to the small size of the grains. Density has also not been experimentally determined, but the calculated value is 9.55 g/cm³. ## Colors and Varieties The observed colors are creamy-white and grayish-white. No varieties of this mineral are distinguished. ## History and Name The name comes from the discovery locality – the Dulanggou gold deposit in Songxian County (Henan Province, China). The mineral was described in 2010 by Zou, Li, and Yu, and approved in the same year by the International Mineralogical Association (IMA2010-025). ## Applications Due to its extreme rarity, dulangouite has no industrial applications. It is solely an object of scientific interest and is valued by collectors specializing in rare minerals and micromounts.

Properties

Luster
Metallic
Density
9.55
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of dulangouite is impossible without advanced analytical techniques. Its recognition is based on chemical analysis using an electron microprobe (EPMA), which confirms the AuTe₂ composition. Visually, it is merely a microscopic, metallic grain with a whitish color. ## Distinguishing from Similar Minerals It can be confused with many other gold and silver tellurides, such as calaverite (AuTe₂), krennerite ((Au,Ag)Te₂), sylvanite ((Ag,Au)Te₂), or petzite (Ag₃AuTe₂), as well as native tellurium. Definitive differentiation is only possible based on chemical composition and crystal structure analysis. Dulangouite is a monoclinic polymorph of calaverite. ## Crystal Forms It occurs exclusively as anhedral (irregular) grains. No well-formed crystals have been observed to date.

Geological environment

## Genesis It forms under low-temperature hydrothermal processes in gold and tellurium deposits. ## Mineral Associations It most commonly co-occurs with native gold, calaverite, petzite, hessite, sylvanite, altaite, coloradoite, pyrite, and quartz. ## Localities The main and only confirmed occurrences are the type locality – the Dulanggou gold deposit in China, and the Trixie mine in Utah, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria For a mineral occurring as microscopic grains, the key criterion is the certainty of identification and the richness of the specimen, i.e., the quantity and size of dulangouite grains. Co-occurrence with other rare tellurides increases its value. ## Popular Localities The most prized specimens come from the type locality in China and from the Trixie mine in the USA, which is its second confirmed occurrence.

Care and storage

## Cleaning Dulangouite specimens are typically micromounts that do not require cleaning. If necessary, dust can be removed with a soft brush or a stream of compressed air. Avoid contact with water and other liquids. ## What to Avoid The mineral is sensitive to acids and other chemical reagents, which can damage it. Ultrasonic cleaners and sudden temperature changes should be avoided. ## Storage The safest storage method is a specialized micromount box, which protects the specimen from dust, moisture, and mechanical damage.

Sources

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