CORONADITE

    Class : Oxides and hydroxides
    Subclass : Oxides
    Crystal system : Monoclinic
    Chemistry : PbMn8O16
    Rarity : Uncommon


Coronadite is an oxide of manganese and lead, sometimes slightly hydrated, frequently showing low iron and aluminum contents. It is a secondary mineral which forms in the upper oxidized part of lead and manganese deposits, perhaps by recrystallization of a lead-bearing psilomelane. It takes its name from its place of discovery : the Coronado vein (Arizona, USA). It is usually massive, constituting botryoidal or nipple-like masses with a fibrous or fibrolamellar texture, with a surface commonly bristling with small crystalline points. Its color is light gray to black, with a semi-metallic to dull luster ; it is distinguished from other manganese oxides by its high density (nearly 5). It is occasionally an ore of manganese and lead.


Main photo : Coronadite from Rosh Pinah Mine, Ilkaras Region, Namibia © Bruce Cairncross

Coronadite from Échassières, Allier, France © Pascal Chollet
Coronadite from Le Kaymar, Aveyron, France © Jean-Marie Boisson
Coronadite from Broken Hill, Australia © Elise Chaigneau & Eric Penet
Coronadite from Bou Tazoult, Morocco © Günter Grundmann

Coronadite in the World

The crystals are rare, the best known come from Bou Tazoult in the Moroccan Anti-Atlas, where coronadite was exploited as manganese and lead ore. It is also known in manganese deposits in the United States, notably those in Arizona (Magma and Coronado mines), Mexico (Talamantes and Ojuela), Australia (Broken Hill), in the gossan of the lead deposit of Mehdi-Abad (Iran) as well as Rosh Pinah Mine (Namibia).

Coronadite in France

In France, coronadite is reported in Crozet (Loire), Kaymar (Aveyron), Echassières (Allier), Peyrebrune (Tarn), Aurouze (Haute-Loire), as well as in many other localities.

Twinning

No twin known for this mineral species.

Fakes and treatments

No fake identified for this mineral species but can be difficult to differentiate from the psilomelane with which it shares its deposits.



Hardness : 4.5 to 5
Density : 5.24 to 5.50
Fracture : Irregular to fibrous
Streak : Brown-black


TP : Opaque
RI : -
Birefringence : -
Optical character : Biaxial
Pleochroism : None
Fluorescence : None


Solubility : -


Magnetism : None
Radioactivity : None