STEWARTITE

    Class : Phosphates, arsenates and vanadates
    Subclass : Hydrated phosphates
    Crystal system : Triclinic
    Chemistry : MnFe2(PO4)2(OH)2 8H2O
    Rarity : Very rare to rare

Stewartite is a rare secondary phosphate of granitic pegmatites. It comes from the alteration of primary phosphates such as triphylite or lithiophilite and usually accompanies other secondary phosphates (heterosite, eosphorite, etc...). Its name comes from its discovery location : the Stewart mine (California). Stewartite forms thin lamellar crystals not exceeding 4 mm, assembled in sheaves or tufts in the fractures of primary phosphates. Stewartite is lemon yellow to brownish yellow in color; it is the polymorph of laueite and pseudolaueite.

Main photo : Stewartite from Hagendorf, Germany © Stephan Wolfsried

Stewartite from Hagendorf, Germany © Stephan Wolfsried
Stewartite from Fletcher Mine, New Hampshire, USA © David L. Busha
Twinned Stewartite from Hagendorf, Germany © Stephan Wolfsried
Stewartite from Collioure, Pyrénées-Orientales, France © Pascale & Daniel Journet

Stewartite in the World

Many specimens of Stewartite come from American phosphate pegmatites in California (Stewart Mine near Pala), South Dakota (Tip Top), Maine, New Hampshire, etc. Good specimens have also been discovered in the pegmatites of Karibib (Namibia) and Sabugal (Portugal).

Stewartite in France

In France, stewartite has been discovered in the Vilate quarry near Chanteloube (Haute-Vienne) and in the pegmatites of Collioure (Pyrénées-Orientales).

Twinning

Twinning is known on {010} forming fish-tails.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : Undetermined
Density : 2.94
Fracture : Undetermined
Streak : White

TP : Translucent to transparent
RI : 1.612 to 1.681
Birefringence : 0.048 to 0.051
Optical character : Biaxial -
Pleochroism : Visible
Fluorescence : None

Solubility : -

Magnetism : NoneRadioactivity : None

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