Giraudite-(Zn)

Chemical formula: Cu¹⁺₆(Cu¹⁺₄Zn²⁺₂)As³⁺₄Se²⁻₁₃

Giraudite-(Zn) is a very rare copper, zinc, and arsenic selenide, forming tiny, metallic-lustered crystals in the isometric system.

## Characteristics Giraudite-(Zn) is a very rare mineral from the tennantite group, belonging to the selenides. It forms very small, idiomorphic crystals with a tetrahedral habit, often not exceeding 100 micrometers. It occurs as inclusions within other minerals. It is opaque and has a black color with a metallic luster. ## Physical Properties Its Mohs hardness is 3.5-4. It has a metallic luster and is opaque. The streak is black. Due to the small size of the crystals, precise determination of density is difficult. ## History and Name The mineral was approved by the IMA in 2018. Its name honors Roland Giraud (born 1941), a French amateur mineralogist who first found this mineral. The suffix "-(Zn)" refers to zinc as the dominant divalent metal in its structure. The type locality is the Chaméane uranium deposit in France.

Properties

Mohs hardness
3.5-4
Luster
Metallic
Streak
Black
Density
0
Transparency
Opaque
Crystal system
Isometric

Diagnostic features

## Identification Identification of giraudite-(Zn) is possible only through advanced laboratory methods, such as chemical analysis (EDS) and X-ray diffraction (XRD), due to its microscopic size and similarity to other sulfides and selenides. Visually, it is characterized by its black color, metallic luster, and tetrahedral crystal habit. ## Differentiation from similar minerals It can be confused with other minerals from the tennantite group, such as tennantite, tetrahedrite, or giraudite-(Fe) itself. Definitive differentiation requires chemical composition analysis to confirm the dominance of zinc and selenium. ## Crystal forms It forms very small, well-formed crystals with a tetrahedral habit, rarely exceeding 100 micrometers. It occurs as single crystals or small aggregates, most often as inclusions in other minerals.

Geological environment

## Genesis It is a mineral of hydrothermal origin. At the type locality (Chaméane, France), it formed in low-temperature hydrothermal veins cutting metamorphic rocks (gneisses). Its formation was associated with uranium mineralization. ## Mineral associations It co-occurs with minerals such as hakite, clausthalite, uraninite, pyrite, chalcopyrite, sphalerite, galena, quartz, and dolomite. ## Localities The only confirmed locality for this mineral worldwide is its type locality: the Chaméane uranium deposit, Le Vernet-Chaméane, Puy-de-Dôme, Auvergne-Rhône-Alpes in France.

Rarity

Extremely rare

For collectors

## Quality criteria As a microscopic mineral, the collector's value of a specimen primarily depends on the confirmation of its identity and the abundance and quality of crystals visible under magnification. Most valued are specimens where the crystals are well-formed, numerous, and contrast with the surrounding rock matrix. Association with other rare minerals is also important.

Care and storage

## Cleaning Due to the extreme rarity and microscopic size of the crystals, mechanical cleaning is neither recommended nor usually possible. Specimens should be protected from dust. ## What to avoid Contact with chemicals, especially acids, which can damage the mineral, should be avoided. Ultrasound and high temperatures should also be avoided. ## Storage Specimens containing giraudite-(Zn) should be stored under stable conditions, in sealed "micromount" containers, to protect them from dust, moisture, and mechanical damage.

External references

Sources

Read more