Barylite
Barylite is an IMA-recognized mineral species in the silicate class, with the chemical formula BaBe₂Si₂O₇.
It crystallizes in the orthorhombic crystal system (space group Pmn2_1).
Key properties: Mohs hardness 7; specific gravity 4.066; Vitreous to greasy luster; optically biaxial.
IMA symbol By, IMA status: approved, named in 1876.
Found in a banded vein in a metamorphosed stratiform zinc orebody (Franklin, New Jersey, USA); in an “amazonite" pocket (Park Co., Colorado, USA); in narrow veins in chertlike silica and albite in fenitized gneisses (Seal Lake, Canada).
It is found associated with Hedyphane (Långban, Sweden); hedyphane, willemite (Franklin, New Jersey); microcline, baryte, fluorite (Park Co., Colorado); eudialyte (Seal Lake, Canada).
Its name comes from the Greek for heavy, for its high density and a suffix for the polytype.