Amarantite - Encyclopedia

    Class : Sulphates, chromates, molybdates
    Subclass : Hydrated sulphates
    Crystal System : Triclinic
    Chemistry : Fe2(SO4)2O 7H2O
    Rarity : Rare

Amarantite is a rare iron sulphate formed by the weathering of iron sulphides in an arid climate. Its name comes from the Latin amarantus (amaranth) in reference to its purple-red color. It is a secondary mineral which is part of a classic mineralogical procession to which other iron sulphides belong (copiapite, voltaite, jarosite, coquimbite, botryogen, fibreferrite, etc...), resulting like it from precipitation from acid natural sulfuric acid, formed by reaction of surface water with iron sulphides. By changing the conditions of the environment (temperature, pH, oxidation-reduction potential, etc...), these sulphates are easily hydrolyzed into ferric hydroxides (goethite, limonite, etc...). Amarantite forms elongated prismatic to acicular crystals, frequently flattened and strongly striated, united in radiating aggregates, of a brownish-red to dark red-orange ("amaranth") tint.

Amarantite from Queténa Mine, Antofagasta, Chile
© Enrico Bonacin
Amarantite from Cuya, Arica, Chile
© Germano Frett

Amarantite from Queténa Mine, Antofagasta, Chile -
© Elmar Lackne
Amarantite from Queténa Mine, Antofagasta, Chile -
© Stephan Wolfsrie

Amarantite in the World

Amarantite is above all a Chilean mineral, known in fine samples in the large copper deposits of northern Chile (Alcaparrosa, Chuquicamata, Sierra Gorda) where the crystals can reach 5 mm; it is also reported in other sites, notably in the Santa Maria Mountains (California, USA), in Kavir-e-Sagand (Iran), in Italy, etc...
 
Main photo : Amarantite from Queténa Mine, Antofagasta, Chile - © Luigi Mattei

Amarantite in France

Amarantite is not reported in the French underground.

Twinning

No twin report for this mineral species.

Fakes and treatments

No fake reported for this species.



Hardness : 2,5
Density : 2,18 to 2,28
Fracture : Irregular
Trace : Yellow




TP : Translucent to transparent
RI : 1.516 to 1.621
Birefringence : 0.105
Optical character : Biaxial -
Pleochroism : Visible
Fluorescence : None


Solubility : Water or hydrochloric acid

Magnetism : None
Radioactivity : None

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