White hexagonal crystals of the very rare franzinite from the type locality (Casa Collina Old Quarry, Pitigliano, Grosseto, Tuscany, Italy) and one of the few localities known worldwide. Sharp franzinite crystals are a very sought after mineral. — Photo: David Hospital · CC BY-SA 4.0
Franzinite
Franzinite is an IMA-recognized mineral species in the silicate class, with the chemical formula (Na,K)₃₀Ca₁₀(Si₃₀Al₃₀)O₁₂₀(SO₄)₁₀·2H₂O.
It crystallizes in the hexagonal crystal system (space group P321). It is a member of the Cancrinite-sodalite structural group.
Key properties: Mohs hardness 5; specific gravity 2.46–2.52; Pearly luster; optically uniaxial.
IMA symbol Frz, IMA status: approved, named in 1976.
Found in ejected metasomatized pumice blocks, thought to be the product of a syntectic process between a trachytic magma and carbonate rocks at the volcanic vent.
It is found associated with Diopside, vesuvianite, afghanite, liottite (Pitigliano, Italy); calcite, leucite (Ariccia, Italy).
The name refers to Marco Franzini, Professor of Mineralogy, University of Pisa, Pisa, Italy.