Dark brown perfect crystals of the extremely rare new mineral theresiaite (IMA 2013-050) from the famous locality La Fossa Crater (Vulcano Island, Aeolian Islands, Sicily, Italy), on adranosite crystals. Formula: (NH4)3KNa2Fe2+Fe3+(SO4)3Cl5. The sample is completely sealed in nitrogen atmosphere, so it is perfectly stable. It is a one locality mineral worldwide, and in La Fossa Crater only a few specimens have been found, so it is a very sought after mineral!. The photo have been made through the plasticbox, so quality is not very high. — Photo: David Hospital · CC BY-SA 4.0
Therasiaite
Therasiaite is an IMA-recognized mineral species in the sulfate class, with the chemical formula (NH₄)₃KNa₂Fe²⁺Fe³⁺(SO₄)₃Cl₅.
It crystallizes in the monoclinic crystal system (space group Cc).
Key properties: Mohs hardness 1.5–2; specific gravity 2.41; Brown streak; Vitreous luster; optically biaxial.
IMA symbol The, IMA status: approved, named in 2013.
A sublimate on pyroclastic breccia in a medium temperature (~250ºC) intracrater active volcanic fumarole.
It is found associated with Salammoniac, kremersite, adranosite.
The name is taken from the type locality, Therasia, one of the ancient names for Vulcano island (from the Greek for “warm earth”).