MCGUINNESSITE

    Class : Carbonates, nitrates, borates
    Subclass : Anhydrous carbonates
    Crystal system : Monoclinic
    Chemistry : (Mg,Cu)2(CO3)(OH)2
    Rarity : Very rare

Mcguinnessite is a very rare secondary carbonate from the oxidation zone of copper deposits, where it is associated with chrysocolla, malachite, goethite and azurite. It was named in honor of the American merchant Albert L. McGuinness who discovered some new species. Macguinnessite forms small fibers united into spherules of 2 mm in diameter maximum. The color, usually blue-green, varies according to the composition, going from a clear blue in the copper terms to a pale blue-green to almost white for the magnesium terms.

Main photo : Mcguinnessite from Lobminggraben, Styria, Austria © Christian Auer

Mcguinnessite from Sierra Magnesite Mine, Gabbs, Nevada, USA © Douglas Merson
Mcguinnessite from Eibenthal, Dubova, Romania © Stephan Wolfsried
Mcguinnessite from the Agoudal mines, Morocco © Jean-Pierre Barral
Mcguinnessite from Oms, Pyrénées-Orientales, France © Johan Rosell

Mcguinnessite in the World

Mcguinnessite is known from around twenty deposits in the world, the most beautiful samples come from Red Mountain (California). The Agoudal mines (Morocco) produced very small prismatic crystals with square sections, which is extremely rare for the species.

Mcguinnessite in France

In France, mcguinnessite is reported in Canari (Haute-Corse) as well as in Oms (Pyrénées-Orientales).

Twinning

No twin known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 2.5
Density : 3.02 to 3.22
Fracture : Undetermined
Streak : White

TP : Translucent
RI : 1.596 to 1.732
Birefringence : 0.128 to 0.130
Optical character : Biaxial -
Pleochroism : Low
Fluorescence : None

Solubility : Acids

Magnetism : NoneRadioactivity : None