Aphthitalite

minerals

sylvite

jarosite

thenardite

Images
Formula: K3Na(SO4)2
Anhydrous normal sulphate
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
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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