DEMESMAEKERITE

    Class : Oxides et hydroxides
    Subclass : Uranyl selenites
    Crystal system : Triclinic
    Chemistry : Pb2Cu5(UO2)2(SeO3)6(OH)6 2H2O
    Rarity : Very rare

The appearance of demesmaekerite and other uranium selenites requires the joint presence of sufficient quantities of selenium and uranium in the same deposit. These conditions are only met exceptionally, which explains the great rarity of these minerals, only four in number (guilleminite, demesmaekerite, derriksite and marthozite), and their presence in only three deposits. It was named in honor of the Belgian geologist Gaston Demesmaeker. Demesmaekerite forms elongated or tabular bottle-green crystals, reaching 1 mm. It dehydrates easily to turn brownish.

Main photo : Demesmaekerite from Musonoi Mine, Kolwezi, Democratic Republic of Congo © Stephan Wolfsried

Demesmaekerite from Musonoi Mine, Kolwezi, D.R. Congo © Stephan Wolfsried
Demesmaekerite from Musonoi Mine, Kolwezi, D.R. Congo © Stephan Wolfsried
Demesmaekerite from Musonoi Mine, Kolwezi, D.R. Congo © Chuck Adan
Demesmaekerite from Musonoi Mine, Kolwezi, D.R. Congo © Vandall Thomas King

Demesmaekerite in the World

It is known in the oxidation zone of the Musonoï copper and cobalt deposit (Democratic Republic of Congo) which provided the best specimens. Selenium comes from the alteration of a seleniferous digenite and uranium from the dissolution of rare uranium minerals. It is also found in Zálesí (Czech Republic) as well as at the Eureka mine (Spain).

Demesmaekerite in France

Demesmaekerite is not present in the French underground.

Twinning

No twin known for this mineral species.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 3 to 4
Density : 5.28
Fracture : Undetermined
Streak : Green

TP : Translucent to opaque
RI : 1.835 to 1.910
Birefringence : 0.075
Optical character : Biaxial +
Pleochroism : Visible
Fluorescence : None

Solubility : -


Magnetism : None
Radioactivity : Medium

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