What is Natrojarosite?
Natrojarosite is the sodium-dominant jarosite-group sulfate formed in acidic oxidation zones and saline, sulfate-rich environments.
Mineralogy and crystal structure
Reference formula: NaFe3(SO4)2(OH)6. Natrojarosite is a trigonal jarosite-group mineral with sodium in the large cation site. Solid solution with jarosite and hydronium jarosite is common, so chemistry and paragenesis matter more than yellow colour alone. Natrojarosite is classified with sulfates and has a trigonal crystal system. Typical hardness is 3–3.5 on the Mohs scale and specific gravity is approximately 2.9–3.2.
Colour, lustre and habit
Typical colours include yellow, brown, orange, greenish. The usual crusty, botryoidal, granular habit and earthy, vitreous, dull lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Natrojarosite forms in or is associated with oxidised sulfide deposits, acid mine drainage, saline soils and weathering zones. Important documented localities include Spain, Australia, Chile, the United States, Mexico and South Africa.
Ochre-yellow chemistry from an acidic ore zone
Natrojarosite is a visible marker of aggressive weathering. Its yellow crusts show how sulfide oxidation, acidity and sodium combine to build a new mineral at the surface.
Collecting and care
Avoid water and acids; keep enclosed and do not generate dust from altered material.
