Outstanding yellow brown crystals of the rare sulphate mineral metasideronatrite from the famous Chuquicamata mine (Chuquicamata Mine, Chuquicamata, Calama, El Loa Province, Antofagasta Region, Chile). — Photo: David Hospital · CC BY-SA 4.0
Metasideronatrite
Metasideronatrite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Na₂Fe³⁺(SO₄)₂(OH)·H₂O.
It crystallizes in the orthorhombic crystal system (space group Pbnm).
Key properties: Mohs hardness 2.5; specific gravity 2.68; Silky luster; optically biaxial.
IMA symbol Mnat, grandfathered status — known before the IMA’s founding, named in 1938.
An uncommon alteration product of pyrite, typically formed in arid climates but stably formed in sea-shore environments.
It is found associated with Sideronatrite, metavoltine, ungemachite, ferrinatrite, alunogen, natrojarosite, pickeringite, sulfur, tamarugite, aluminocopiapite, metavoltine, mendozite.
Its name comes from the Greek meta, signifying a lower hydrate, and its relation to sideronatrite.