Garnierite - Encyclopedia

    Class : -
    Subclass : -
    Crystal system : -
    Chemistry : -
    Rarity : Uncommon

Garnierite is a general term designating a nickel ore composed of different hydrated nickel silicates and which owes its name to the French Mining Engineer Jules Garnier. These nickel silicates are formed during surface alteration at the expense of peridotites and dunites, rocks without expressed nickel minerals but composed mainly of orthorhombic pyroxenes and olivines which contain respectively 0.5% NiO and 0.6% NiO. The process of surface alteration destroys these minerals and enriches the emerging lateritic crust with nickel where this metal integrates the crystal lattice of newly formed hydrated silicates : garnierites.

Newly formed garnierites are either clay minerals, notably nickel saponites, or serpentines. Garnierite is also a term sometimes wrongly attributed to a serpentine with the formula (Ni,Mg)3(Si2O5)(OH)4. More strictly, these are nickel-bearing varieties of chrysotile or antigorite, or nepouite, which is a true nickel-bearing mineral of the serpentine group.

The term "noumeite" (in allusion to Nouméa and the very important lateritic nickel deposits of New Caledonia) is sometimes used to designate particularly rich garnierites, grading between 10 and 30% nickel.

Garnierite constitutes compact to powdery masses, with a talcose feel, of a beautiful characteristic apple green color. Intimate mixing with iron oxides can, however, result in a brown to painted ore tinged with greenish. It is an essential mineral, at least as important in terms of production as nickel from sulphide deposits. Polished can also be used in jewelry.

Main photo : Garnierite from the Camp des Sapins Mine, New Caledonia, France © Cédrick Gineste

Garnierite in the World

Garnierite is present in many locations around the world such as Australia (Scotia Nickel Mine), China (Jinchang Mine, Yunnan), Indonesia (Sorowako) and the USA (Josephine Creek Mining, Oregon).

Garnierite in France

The best samples of garnierite in the world are French and come from New Caledonia (Népoui Mine, Camp des Sapins Mine, Barbouilleurs Mine, etc...).

Right photo : Garnierite from the Camp des Sapins Mine, New Caledonia, France © Cédrick Gineste

Fakes and treatments

No fakes recorded for this mineral species.

Hardness : 2 to 2.5
Density : 3.24
Fracture : Irregular
Streak : White-green

TP : Translucent to opaque
RI : 1.576 to 1.650
Birefringence : 0.027
Optical character : Biaxial -
Pleochroism : Low
Fluorescence : None

Solubility : -

Magnetism : None
Radioactivity : None


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