CONICHALCITE

    Class : Phosphates, arsenates, vanadates
    Subclass : Anhydrous arsenates
    Crystal system : Orthorhombic
    Chemistry : CaCu(AsO4)(OH)
    Rarity : Uncommon

Conichalcite is a fairly common secondary arsenate from the oxidation zone of arsenic-rich copper deposits, associated with tyrolite, lavendulanite and olivenite. Its name comes from the Greek konis (dust) and khalkos (copper) in reference to its habitus and its chemical composition. Its crystals are extremely rare and always tiny, short prismatic, or isometric. Conichalcite generally appears in bright submillimeter globules and botryoidal or nipple-like encrustations with a fibroradiated structure. Its color, apple green, grass green, or pistachio green, is characteristic.

Main photo : Conichalcite from Gold Hill Mine, Utah, USA © Stephan Wolfsried

Conichalcite from Tintic Mine, Utah, USA © Jerry A. Baird
Conichalcite from Cerro Minado Mine, Andalusia, Spain © Miguel Segura
Conichalcite from Cabeça Alta Mine, Évora, Portugal © Pedro Alves
Conichalcite from Valzergues, Aveyron, France © Patrice Queneau

Conichalcite in the World

The best known crystals come from the United States. The Higgins mine (Bisbee, Arizona) produced millimeter crystals considered to be the best in the world, while the Utah mines (Tintic, Gold Hill, etc.) provide abundant hilly spherolitic aggregates grouped in encrustations, resulting from the alteration of enargite. The copper deposits of Mexico (Mapimi in particular), Namibia (Tsumeb) and Iran (Talmessi) produced apple green globules making up good quality specimens.

Conichalcite in France

In France, conichalcite in spherules of 1 mm in diameter is found relatively abundantly at the Cap Garonne mine (Var), on certain fluorites at Valzergues (Aveyron) as well as apple green encrustations at Anozel (Vosges), at the St Estèbe quarry near Narbonne (Aude)

Twinning

A rare twin is known on {001}.

Fakes and treatments

No fake identified for this mineral species.


Hardness : 4.5
Density : 4.33
Fracture : Irregular
Streak : Green

TP : Translucent to transparent
RI : 1.778 to 1.846
Birefringence : 0.034
Optical character : Biaxial (+/-)
Pleochroism : Visible
Fluorescence : None

Solubility : Nitric acid and hydrochloric acid


Magnetism : None
Radioactivity : None

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