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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).
Localities
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).
Natrojarosite from the Francon Quarry -
Image
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).
At the Kutch District, Gujarat, India, the mineralogy and unit-cell parameters indicate
supergene or
hydrothermal alteration conditions within the region. The
occurrences of natrojarosite and associated natroalunite and
kaolinite in the post-Deccan volcanic province are consistent with an
oxidising environment and periodic shift of humid to arid environments that appear to be similar to the early
geologic history of Mars. The oxidative alteration of pyrite further enhances
the formation of natrojarosite. The natrojarosite and the associated minerals (including
anhydrite and other sulphates) argue for acidic and water-limited
conditions analogous to the Noachian-Hesperian epoch of Mars
(AM 110.10.1516-1526).
The type locality is Soda Springs Valley, Mineral county, Nevada, USA.
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