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Formula: K3Na(SO4)2
Anhydrous sulphate, aphthitalite group
Specific gravity: 2.66 to 2.71
Hardness: 3
Streak: White
Colour: Colourless (rare), white, grey, bluish, greenish, reddish; colourless in transmitted light
Solubility: Soluble in water and in acids
Environments:
Evaporite Deposits
Cave deposits
Fumeroles
Aphthitalite occurs in two different environments. It is formed in volcanoes as uncommon incrustations in
fumeroles, where
it may deposit from volcanic gas during cooling from about 800oC down to 400oC,
together with thénardite.
It also occurs in marine and continental evaporite deposits
(Dana, Webmin, Mindat, HOM). A third occurrence is in guano deposits, which are typically ammonian
(HOM).
In fumeroles it is associated with thénardite,
jarosite, sylvite and
hematite. In evaporites it is associated with
blödite, syngenite,
mirabilite, picromerite,
borax and halite. In guano deposits
it is associated with syngenite,
whitlockite, monetite,
niter and gypsum
(HOM).
Localities
At the type locality, Mount Vesuvius, Somma-Vesuvius Complex, Naples, Campania, Italy, aphthitalite occurs
in volcanic fumaroles associated with thénardite,
sylvite, jarosite and
hematite
(Mindat).
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