Images
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
Environments
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