Ferrimolybdite - Encyclopedia

    Class : Sulfates, chromates, molybdates
    Subclass : Molybdates
    Crystal system : Orthorhombic
    Chemistry : Fe2(MoO4)3 8H2O
    Rarity : Uncommon

Ferrimolybdite is the classic alteration mineral of molybdenum sulfides, it is found in the oxidation zone of hydrothermal molybdenum deposits. Its name is linked to its chemical composition (iron + molybdenum). Its usual appearance is that of a yellow to grayish-brown powder covering the molybdenite, but it can also appear in sheaves, in packets or in radiated aggregates of fine translucent canary yellow needles.

Main photo : Ferrimolybdite from Ochtiná, Slovakia © Martin Stevko

Ferrimolybdite on molybdenite from Holts Ledge, New Hampshire, USA © Peter Cristofono
Ferrimolybdite from Ochtiná, Slovakia © Martin Stevko
Ferrimolybdite from Ochtiná, Slovakia © Martin Stevko
Ferrimolybdite from Château-Lambert, Haute-Saône, France © Andrea Schloth

Ferrimolybdite in the World

Ferrimolybdite was relatively abundant in the Climax molybdenite mine (Colorado). It is known in most molybdenum mines in the United States and Australia (Kingsgate, Three Springs). Beautiful crystallizations were also discovered in Ochtiná (Slovakia) and at the Vrchoslav fluorite mine (Czech Republic).

Ferrimolybdite in France

In France, ferrimolybdite was discovered in crystals in the tourmalinites of Teillou, near Brillac (Charente), and in the copper and molybdenum mine of Château-Lambert (Haute-Saône).

Twinning

No twin known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 1 to 2
Density : 2.99
Fracture : Underterminated
Streak : Pale yellow

TP : Translucent to transparent
RI : 1.720 to 2.040
Birefringence : 0.130 to 0.230
Optical character : Biaxial +
Pleochroism : Visible
Fluorescence : None

Solubility : Hydrochloric acid


Magnetism : None
Radioactivity : None