STRENGITE

    Class : Phosphates, arsenates, vanadates
    Subclass : Hydrated phosphates
    Crystal system : Orthorhombic
    Chemistry : FePO4 2H2O
    Rarity : Rare

Strengite is a secondary phosphate of granitic pegmatites, more rarely gossans or limonitized iron deposits. It is the dimorph of phosphosiderite. It comes from the alteration of primary phosphates (triphylite or lithiophilite), and usually accompanies other secondary phosphates (heterosite, eosphorite). It was named in honor of Johann August Streng, Professor of Mineralogy at the University of Giessen (Germany). Strengite forms lamellar crystals, sometimes elongated, not exceeding 5 cm, more frequently spherulites or botryoidal masses with a fibroradiated texture. The mineral is purple, violet to carmine red in color, sometimes pinkish-orange or greenish.

Main photo : Strengite from Indian Mountain, Alabama, USA © Jason B. Smith

Strengite from Indian Mountain, Alabama, USA © Henry Barwood
Strengite from Indian Mountain, Alabama, USA © Stephan Wolfsried
Green strengite on quartz from Echassières, Allier, France © Yannick Vessely
Strengite & cacoxenite from La Fumade, Tarn, France © Pascal Chollet

Strengite in the World

The most beautiful specimens of strengite come from the Bull Moose pegmatite near Custer (South Dakota) and Rock Run Station (Alabama), where purple crystals reaching 5 cm were discovered. The pegmatites of Hagendorf and Kreuzberg near Pleystein (Bavaria, Germany), have given spectacular groups of purplish crystals. Other American pegmatites from California, Arkansas, Pennsylvania have also provided interesting samples of strengite. The large Australian iron deposit of Iron Monarch near Iron Knob, as well as the German iron deposits of the Giessen region in Hesse also contain fine specimens of this mineral.

Strengite in France

In France, strengite is known at Echassières (Allier), in the pegmatites of Chanteloube (Haute-Vienne) and Collioure (Pyrénées-Orientales), at La Fumade (Tarn), at the quarry of La Lande (Morbihan) and at the Birrity quarry (Pyrénées-Orientales).

Twinning

Twinning is known but rare on {201}.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 3.5 to 4
Density : 2.84 to 2.87
Fracture : Undetermined
Streak : White

TP : Translucent to transparent
RI : 1.697 to 1.745
Birefringence : 0.044
Optical character : Biaxial -+
Pleochroism : None
Fluorescence : None

Solubility : Hydrochloric acid

Magnetism : NoneRadioactivity : None

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