White crystal aggregates of the extremely rare mineral matteuccite from the type locality in Italy (Monte Somma, Vesuvius, Campania, Italy) and only one of the two known localities worldwide. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Matteuccite
Matteuccite is an IMA-recognized mineral species in the sulfate class, with the chemical formula NaH(SO₄)·H₂O.
It crystallizes in the monoclinic crystal system (space group Cc).
Key properties: specific gravity 2.118; optically biaxial.
IMA symbol Mtt, grandfathered status — known before the IMA’s founding, named in 1952.
Found in stalactites formed in a volcanic crater.
It is found associated with Mercallite, ralstonite.
The mineral was named to honor Vittorio Matteucci (1862–1909), Director of the Vesuvius Laboratory, Vesuvius, Italy.