Fornacite - Encyclopedia
Class : Sulfates, chromates, molybdates
Subclass : Chromates
Crystal system : Monoclinic
Chemistry : Pb2Cu(AsO4)(CrO4)(OH)
Rarity : Very rare
Fornacite is a rare chromate and arsenate of lead and copper whose genesis is conditioned by an arid climate. It is found associated with wulfenite, mimetite, sometimes dioptase, in the oxidation zones of lead, zinc and copper deposits. It was named in honor of Lucien Louis Fourneau, colonial governor of the French Congo where the mineral was discovered. Dark green in color, fornacite forms small prismatic crystals ending in pointed pyramids, it can also be lamellar to acicular. The crystals are usually grouped together.
Main photo : Fornacite de Renéville, Kindanba District, Democratic Republic of Congo © Andreas Schloth
Fornacite in the World
Twinning
No twin known for this mineral species.
Fakes and treatments
No fakes recorded for this mineral species.
Hardness : 2 to 3
Density : 6.27
Fracture : Irregular to conchoidal
Streak : Olive green
TP : Transparent
RI : 2.142 to 2.242
Birefringence : 0.100
Optical character : Biaxial +
Pleochroism : None
Fluorescence : None
Solubility : Hydrochloric acid
Magnetism : None
Radioactivity : None