Fairfieldite - Encyclopedia

    Class : Phosphates, arsenates, vanadates
    Subclass : Hydrated phosphates
    Crystal system : Triclinic
    Chemistry : Ca2(Mn,Fe)(PO4)2 2H2O
    Rarity : Rare

Fairfieldite is a hydrated phosphate accessory to granitic pegmatites, in which it is associated with numerous other primary and secondary phosphates (eosphorite, lithiopyllite, etc...). It owes its name to its location of discovery : Branchville in Fairfield County (Connecticut, USA). Fairfieldite occurs in prismatic to equant crystals, frequently united in foliated, fibrous or lamellar aggregates, or in masses with a radiated texture. Its color is white or embellished with yellowish, greenish-white or orange-pink pastel tones.

Main photo : Fairfieldite of Foote, North Carolina, USA © Rob Lavinsky

Fairfieldite from Foote, North Carolina, USA © Jason B. Smith
Fairfieldite and eosphorite from Estes Quarry, Baldwin, Maine, USA © Stephan Wolfsried
Fairfieldite from Foote, North Carolina, USA © Stephan Wolfsried
Fairfieldite from LCA Mine, Gaston County, North Carolina, USA © Knut Eldjarn

Fairfieldite in the World

The American pegmatites of South Dakota (Tip-Top and Bull Moose, near Custer) yielded centimeter-sized crystals (maximum 2.8 cm) which are the best specimens in the world. Those of Maine (Rumford, Buckfield, etc.) contain similar quality crystals. Fairfieldite is also present in the lithiniferous pegmatite of Foote (North Carolina) and in the classic European pegmatites of Hagendorf near Pleystein (Bavaria, Germany) and Mangualde (Portugal).

Fairfieldite in France

Fairfieldite is not present in the French underground.

Twinning

No twin known for this mineral species.

Fakes and treatments

No fake listed for this mineral species.


Hardness : 3.5
Density : 3.08 to 3.11
Fracture : Irregular
Streak : White

TP : Translucent to transparent
RI : 1.633 to 1.660
Birefringence : 0.019 to 0.020
Optical character : Biaxial +
Pleochroism : None
Fluorescence : None

Solubility : Acids


Magnetism : None
Radioactivity : None

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