Formula: Na2Fe3+(SO4)2(OH).3H2O
Hydrated sulphate containing hydroxyl
Crystal System: Orthorhombic
Specific gravity: 2.22 to 2.35 measured, 2.276 calculated
Hardness: 1½ to 2
Streak: Yellowish white
Colour: Yellow, yellow-brown, straw-yellow, light orange, pale yellow to nearly colourless in transmitted light
Solubility: Insoluble in cold water. Decomposed in boiling water with separation of ferric oxide.
Common impurities:

Hydrothermal environments

Sideronatrite is an uncommon secondary mineral in the oxidised zone of iron-rich deposits in very arid climates; it may be a post-mine mineral. It is also formed by alteration of pyrite by saline water in metallic veins, coal measures and sea-spray environments. Associated minerals include metasideronatrite, ferrinatrite, copiapite, voltaite, melanterite, halotrichite, uklonskovite, jurbanite, jarosite, pyrite and marcasite (HOM ). It reversibly dehydrates to metasideronatrite depending on relative humidity and exposure to sunlight (Mindat).


At Potosi, Brazil, sideronatrite occurs with voltaite (Dana).

At the type locality, the San Simon mine, Santa Rosa-Huantajaya mining district, Iquique Province, Tarapacá, Chile, b>sideronatrite occurs in the oxidised zone of iron-rich deposits in very arid regions or as a post-mine product. it is also formed by pyrite oxidation by saline water in veins, coal deposits and near-sea areas, Associated minerals include voltaite, uklonskovite, pyrite, metasideronatrite, melanterite, marcasite, jurbanite, jarosite, halotrichite, ferrinatrite and copiapite (Mindat).

At the Urus plateau, Cheleken peninsula, Balkan, Turkmenistan, sideronatrite occurs with melanterite (Dana).

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