Formula: NaFe3+3(SO4)2(OH)6
Sulphate, alunite group, forms a limited solid solution with jarosite
Crystal System: Trigonal
Specific gravity: 3.183.18 measured, 3.29 calculated
Hardness: 2½ to 3½
Streak: Light yellow
Colour: Yellow, golden brown, red-brown
Solubility: Slowly soluble in hydrochloric acid

Hydrothermal environments
Volcanic sublimates

Natrojarosite is formed typically in the oxidised zone of mineral deposits by alteration of pyrite in the presence of sodium; rarely as a volcanic sublimate. Associated minerals include gypsum, alunite, jarosite and plumbojarosite (HOM).

At Tom's quarry, Kapunda, Mount Lofty Ranges, South Australia, natrojarosite is associated with leucophosphite and natrodufrénite in cavities in goethite-rich rocks (AJM 17.1.29)

At Mount Moliagul, Moliagul, Central Goldfields Shire, Victoria, Australia, aggregates of small crystals or crusts of natrojarosite are found in cavities in quartz, often associated with jarosite (AJM 21.1.43).

At the Francon quarry, Montreal, Quebec, Canada, natrojarosite occurs as an alteration crust on marcasite, and rarely on pyrite. It has also been observed on sphalerite in quartz-lined fractures (MinRec 37.1.40).

At Chuquicamata, near Calama, in Northern Chile, natrojarosite is associated with chalcanthite, kröhnkite and sulphur. It is a late mineral, forming after most of the iron sulphates and before most of the copper sulphates (AM23.669).

The type locality is Soda Springs Valley, Mineral county, Nevada, USA.

Back to Minerals