Outstanding yellow crystals of the sideronatrite, from a new discovery in Spain: Ferruginosa Mine, Cabo de Palos, Murcia, Spain. — Photo: David Hospital · CC BY-SA 4.0
Sideronatrite
Sideronatrite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Na₂Fe³⁺(SO₄)₂(OH)·3H₂O.
It crystallizes in the orthorhombic crystal system (space group Pbnm).
Key properties: Mohs hardness 1.5–2.5; specific gravity 2.22–2.35; Pale yellow streak; Vitreous luster; optically biaxial.
IMA symbol Snat, grandfathered status — known before the IMA’s founding, named in 1878.
Occurs as an uncommon secondary mineral in the oxidized zone of iron-rich deposits in very arid climates, may be post-mine; also produced through alteration of pyrite by saline water in metallic veins, coal measures.
It is found associated with Metasideronatrite, ferrinatrite, copiapite, voltaite, melanterite, halotrichite, uklonskovite, jurbanite, jarosite, pyrite, marcasite.
Its name comes from the Greek for iron, sideros, and sodium, natrium, in its chemical composition.