KIDWELLITE

    Class : Phosphates, arsenates, vanadates
    Subclass : Hydrated phosphates
    Crystal system : Monoclinic
    Chemistry : NaFe9(PO4)6(OH)10 5H2O
    Rarity : Rare

Kidwellite is a secondary phosphate of sodium and iron which forms by alteration and replacement of primary phosphates ; it is found more rarely in granitic phosphate pegmatites. It was named in honor of the American geologist Albert Lewis Kidwell who discovered the mineral. Kidwellite forms tiny acicular crystals gathered in fluffy rosettes, encrustations or spherolitic to botryoidal masses, yellow to pale greenish in color, sometimes greenish white.

Main photo : Kidwellite from Clara Mine, Germany © Michael Förch

Kidwellite from Clara Mine, Germany © Volker Heck
Kidwellite from Indian Mountain, Alabama, USA © Henry Barwood
Kidwellite from Echassières, Allier, France © Michael Förch
Kidwellite from Echassières, Allier, France © Pascal Chollet

Kidwellite in the World

Kidwellite is known in many phosphate geological contexts, notably iron phosphate deposits : Waldgirmes near Giessen (Hesse, Germany), Iron Monarch near Iron Knob (Australia), and the fairly frequent deposits of Arkansas, Virginia and Alabama. Kidwellite is also present in rare phosphate pegmatites (Karibib, Namibia) and in the superficial part of metalliferous deposits such as Broken Hill (Australia) or Wittichen (Germany).

Kernite in France

In France, kidwellite is known at Echassières (Allier) in small pale green spherolites.

Twinning

No twins known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 3
Density : 3.04 to 3.3
Fracture : Irregular
Streak : Yellow

TP : Translucent to opaque
RI : 1.787 to 1.805
Birefringence : 0.018
Optical character : Biaxial -
Pleochroism : None
Fluorescence : None

Solubility : -

Magnetism : NoneRadioactivity : None