MILLERITE

    Class : Sulfides and sulfosalts
    Subclass : Sulfides
    Crystal system : Trigonal
    Chemistry : NiS
    Rarity : Uncommon

Millerite is an hydrothermal mineral which is mainly found in metalliferous nickel deposits and certain coal deposits. It was named in honor of the English mineralogist William Hallowes Miller, Professor at the University of Cambridge who was the first to study the crystals of this mineral. With a metallic luster, millerite is brass yellow to bronze yellow, becoming iridescent in the air. This mineral appears in fine acicular crystals grouped in clumps or in compact masses with a fibrous appearance. Millerite is too scarce, so it is never exploited just for its own sake. It nonetheless constitutes an interesting nickel ore.

Main photo : Millerite from Meikle Mine, Nevada, USA © AM Mizunaka

Millerite from Friedrich Mine, Germany © Rob Lavinsky
Millerite from Keokuk County, Iowa, USA © AM Mizunaka
Millerite from Tiébaghi Nickel Mine, New-Caledonia, France © Jean-Marc Johannet
Millerite from La Buscalie, Aveyron, France © Pascal Chollet

Millerite in the World

The best crystallized samples of millerite come from Germany, mainly from the Siegen district (8 cm acicular crystal masses), Wissen and Ramsbeck (20 cm crystals embedded in sphalerite). Good samples also come from the United States, from the Sterling mine (Antwerp, New York : divergent clumps of acicular crystals reaching 5 cm), from the Keokuk deposits (Iowa), from Meikle Mine (Nevada) and from Lancaster County (Pennsylvania), which provide in abundance masses of acicular crystals.

Millerite in France

In France, millerite is known in La Buscalie near Decazeville (Aveyron), as well as in many deposits. It is also found on the nickel deposits of New Caledonia.

Twinning

No twin known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 3 to 3.5
Density : 5 to 5.5
Fracture : Irregular
Streak : Greenish black

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

Solubility : -

Magnetism : NoneRadioactivity : None