Silvialite
Silvialite is an IMA-recognized mineral species in the silicate class, with the chemical formula Ca₄Al₆Si₆O₂₄(SO₄).
It crystallizes in the tetragonal crystal system (space group I4/m). It is a member of the Scapolite structural group.
Key properties: Mohs hardness 5.5; specific gravity 2.75; White streak; Subvitreous luster; optically uniaxial.
IMA symbol Slv, IMA status: approved, named in 1998.
Found in granulite facies metamorphic rocks, in mafic and ultramafic xenoliths from the lower crust or upper mantle, and in anorthosites in a meteorite-impact structure.
It is found associated with Plagioclase (An45), calcic amphibole, clinopyroxene, garnet, spinel with exsolved ilmenite (McBride Province).
The mineral was named to honor Silvia Hillebrand, daughter of Tschermak, the second ‘l’ in the name added to the conventional ‘ite’ ending to denote a mineral name.