Vésigniéite

Chemical formula: Cu<sup>2+</sup><sub>3</sub>Ba(V<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>(OH)<sub>2</sub>

Vésigniéite is a rare copper and barium vanadate, prized by collectors for its intense green color and characteristic tabular crystals.

## Characteristics Vésigniéite is a mineral from the vanadate group, whose chemical composition includes copper, barium, and vanadate groups. It most often forms thin, tabular or platy crystals with a hexagonal outline, rarely exceeding 1-2 mm. It typically occurs as rosette-like or radial aggregates, as well as crusts and coatings on the host rock. Its intense, vivid color makes it easily noticeable despite the small size of its crystals. ## Physical Properties This mineral is characterized by a Mohs hardness of 3.5-4. It has a relatively high density, ranging from 4.55 to 4.66 g/cm³, which is palpable even in small specimens. The luster is most often vitreous, sometimes with a resinous or greasy tint. It is a brittle mineral with an uneven fracture. ## Colors and Varieties The color of vésigniéite is its most characteristic feature. It ranges from yellowish-green, through grass-green, to olive-green. No named color varieties or commercial names are distinguished for it. ## History and Name The mineral was first described in 1955 by Claude Guillemin. The name comes from Jean Paul Louis Vésignié (1870-1954), a French engineer, mycologist, and president of the French Mineralogical Society, who was the first to collect samples of this mineral. ## Uses Due to its rarity and small crystal size, vésigniéite has no industrial application. However, it is a valued and sought-after collector's mineral.

Properties

Mohs hardness
3.5-4
Luster
Vitreous to resinous
Streak
Yellowish-green
Density
4.55-4.66
Cleavage
Good on {001}
Fracture
Uneven
Transparency
Translucent to opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Key diagnostic features include its intense green color, characteristic hexagonal, tabular crystals forming rosette aggregates, and high density. The mineral rapidly dissolves in hydrochloric acid, which is a strong diagnostic indicator but destroys the sample. ## Distinguishing from Similar Minerals It can be confused with other green secondary copper minerals such as malachite, brochantite, or tyrolite. It is distinguished from malachite by its lack of reaction with acids (malachite effervesces), and from tyrolite and brochantite by its different crystal habit – vésigniéite forms pseudohexagonal tablets, while the others have acicular or platy habits. Chemical analysis confirming the presence of vanadium and barium is also helpful. ## Crystal Forms Crystals are most often thin-tabular, with a pseudohexagonal (six-sided) outline. They usually occur as fan-shaped, rosette-like, or radial aggregates. It also forms granular, massive aggregates, and thin crusts.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation (weathering) zones of ore deposits containing copper, barium, and vanadium. It forms as a result of surface waters acting on the primary minerals of these elements. It often occurs in quartz veins or in cavities of sedimentary rocks, such as sandstones. ## Mineral Associations It co-occurs with other secondary minerals such as malachite, tyrolite, chrysocolla, as well as with calcite, quartz, barite, and various iron and manganese oxides.

Rarity

Rare

For collectors

## Quality Criteria The most highly valued vésigniéite specimens are characterized by sharply formed, lustrous crystals of intense, emerald-green color. Rich groups of crystals forming rosettes or fans, well contrasted with a light host rock, are particularly sought after. The size of the crystals and entire aggregates also significantly affects the value. ## Popular Localities Specimens from the Friedrichssegen mine in Germany are considered the best in the world, setting the standard for this mineral. High-quality material, often in the form of rich crusts, also comes from the Mashamba West mine in the DRC. Czech and French localities usually provide smaller, but still valued specimens.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft brush to remove dust. Due to its reactivity, contact with water, especially acids, should be avoided. If liquid is necessary, isopropyl alcohol can be carefully applied, ensuring quick evaporation. ## What to Avoid All chemical agents, especially acids (even diluted), which rapidly dissolve it, must be strictly avoided. The mineral is sensitive to high temperatures and humidity. It should not be exposed to prolonged direct sunlight, which can cause fading. ## Storage It is recommended to store specimens in a dry place, preferably in closed, padded collector's boxes or display cases, to protect them from dust, moisture, and mechanical damage. The brittleness of the mineral requires careful handling.

Sources

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