Phosphosiderite - Encyclopedia

    Class : Phosphates, arsenates, vanadates
    Subclass : Hydrated phosphates
    Crystal system : Monoclinic
    Chemistry : FePO4 2H2O
    Rarity : Fairly common

Phosphosiderite is a secondary phosphate of granitic pegmatites, more rarely a component of soils. It is the dimorph of strengite and probably forms a complete series with metavariscite. It owes its name to its chemical composition : phosphorus and iron (sideros in Greek). Phosphosiderite comes from the alteration of primary phosphates such as triphylite or lithiophyllite and usually accompanies other secondary phosphates (heterosite, leucophosphite, etc...). It forms tabular crystals with squat prismatic, more frequently encrustations or botryoidal masses with fibrous textures. The mineral is variable in color but often striking : purple, blue-violet to carmine red and pink, sometimes pinkish-orange or greenish, rarely colorless. It is a mineral that is cut into cabochons for jewelry, and used as an ornamental stone.

Phosphosiderite in the World

The most beautiful specimens come from the Bull Moose pegmatite, near Custer (South Dakota) : they are purple crystals up to 2.5 cm. But phosphosiderite is also present in the majority of the famous American phosphate pegmatites of South Dakota, New Hampshire and California. The pegmatites of Hagendorf and Kreuzberg, near Pleystein (Bavaria, Germany) gave spectacular groups of purplish crystals, as did the Brazilian pegmatites of the district of Galileia, in Minas Gerais. This mineral is also found in other large fields of phosphate pegmatites, notably in Mozambique (Muiâne) and Portugal (Mangualde).

Phosphosiderite in France

In France, phosphosiderite is reported in the pegmatite of La Vilatte and Pecout (Haute-Vienne) but also in Echassières (Allier) and in the pegmatite field of Collioure (Pyrénées-Orientales).


Interpenetration twins on {101} are known.

Fakes and scams

No fake recorded for this mineral species.

Hardness : 3.5 to 4
Density : 2.76
Fracture : Irregular
Trace : White

TP : Translucent to transparent
IR : 1.692 to 1.738
Biréfringence : 0.046
Optical character : Biaxial -
Pleochroism : Visible
Fluorescence : None

Solubility : Hydrochloric acid

Magnetism : None
Radioactivity : None


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