Ammoniovoltaite
Ammoniovoltaite is an IMA-recognized mineral species in the sulfate class, with the chemical formula (NH₄)₂Fe²⁺₅Fe³⁺₃Al(SO₄)₁₂(H₂O)₁₈.
It crystallizes in the cubic crystal system (space group Fd3c). It is a member of the Voltaite structural group.
Key properties: Mohs hardness 3–3.5; specific gravity 2.529; Vitreous luster.
IMA symbol Avlt, IMA status: approved, named in 2017.
Occurs as efflorescence that covers walls in cracks around gas/steam (∼100°C.) vents in strongly hydrothermally-altered andesite-basalt in a geothermal region characterized by a high ammonium concentration.
It is found associated with Alunogen, tschermigite, pyrite.
Emphasizes that this is the ammonium analogue of voltaite.
Index entry. This entry combines official IMA/RRUFF species data with published physical-property data — a full written entry hasn’t been published yet.
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