Eldragónite

Chemical formula: Cu₆BiSe₄(Se₂)

Eldragónite is a very rare copper bismuth selenide, forming metallic, black, acicular crystals.

## Characteristics Eldragónite is a very rare mineral from the sulfide group, more specifically a complex copper bismuth selenide. It occurs as very small, acicular or bladed crystals, rarely exceeding 1 mm in length. It forms fibrous aggregates, radial aggregates, or occurs as inclusions in other minerals, mainly umangite. It is opaque and has a black color with a metallic luster. ## Physical Properties This mineral is characterized by a metallic luster and a black streak. Its hardness and density have not been precisely measured due to the small size of the crystals, but the density calculated based on the chemical formula and unit cell parameters is 7.18 g/cm³. It exhibits perfect cleavage in one direction. ## History and Name Eldragónite was discovered in the El Dragón mine in the Potosí Department, Bolivia. Its name comes directly from its type locality. It was approved as a new mineral by the International Mineralogical Association (IMA) in 2011 (IMA2011-088). It was described by a team of mineralogists led by Werner H. Paulus. ## Uses Due to its extreme rarity and microscopic size, eldragónite has no industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized collectors of rare minerals (so-called "micromounts").

Properties

Mohs hardness
3.5
Color
Brownish to light-maroon
Luster
Metallic
Streak
Brownish black
Density
6.76
Cleavage
Perfect on {100}
Fracture
Irregular/Uneven,Conchoidal
Transparency
Opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification Identification of eldragónite is possible almost exclusively using advanced laboratory methods, such as chemical analysis (EDS) and X-ray diffraction (XRD). Visually, on a micro scale, it can be suspected based on its form – black, metallic, acicular or bladed crystals – and its co-occurrence with other selenides in the El Dragón mine. ## Distinguishing from Similar Minerals Eldragónite is very similar to other rare, acicular bismuth selenides and sulfides. It can be confused with watkinsonite, emplectite, or other minerals from the chalcostibite group. Definitive differentiation requires specialized chemical composition analysis, which will show the presence of selenium and the characteristic copper to bismuth ratio. ## Crystal Forms This mineral forms elongated, acicular or bladed crystals, reaching up to 1 mm in length and only a few micrometers thick. Crystals often form chaotic aggregates, fibrous aggregates, or radial rosettes. They occur as inclusions in other minerals, mainly umangite.

Geological environment

## Genesis Eldragónite forms under hydrothermal conditions, in selenium-rich veins. Its formation is associated with crystallization from solutions saturated with copper, bismuth, and selenium at relatively low temperatures. It occurs in association with other selenides in sandstone deposits of the El Fraile formation. ## Mineral Associations This mineral occurs in close association with other selenides. It is most commonly accompanied by umangite (in which it often forms inclusions), klockmannite, berzelianite, clausthalite, eucairite, as well as hematite and quartz. ## Localities The only confirmed locality of eldragónite in the world is its type locality – the El Dragón mine, located in Antonio Quijarro Province, Potosí Department, Bolivia.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of eldragónite specimens is primarily assessed based on the richness and visibility of its microscopic crystals on the rock matrix. Specimens where it forms dense, radial aggregates or well-formed, individual needles are most valued. Association with other rare selenides is also important, increasing the scientific and collectible value of the specimen. ## Popular Localities All eldragónite specimens available on the collector's market come from a single location in the world: the El Dragón mine in Bolivia. This is the only known locality for this mineral.

Care and storage

## Cleaning Specimens of eldragónite should generally not be cleaned mechanically or chemically due to their delicacy and microscopic crystal size. Any attempts at cleaning can easily destroy the delicate needles. If dust removal is necessary, a gentle stream of compressed air can be used from a safe distance. ## What to Avoid Avoid contact with any chemicals, acids, and detergents. The mineral is sensitive to oxidation, so it should be protected from moisture and sudden temperature changes. It should not be washed in water or cleaned with ultrasonics. ## Storage Eldragónite specimens, typically micromounts, should be stored in stable conditions, in closed, airtight "perky boxes". This protects the delicate crystals from mechanical damage, dust, and changes in humidity that could lead to its slow decomposition.

External references

Sources

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