Walstromite
Walstromite is an IMA-recognized mineral species in the silicate class, with the chemical formula BaCa₂Si₃O₉.
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Margarosanite structural group.
Key properties: Mohs hardness 3.5; specific gravity 3.67; White streak; Subvitreous, pearly on cleavages luster; optically biaxial.
IMA symbol Ws, IMA status: approved, named in 1964.
Disseminated in a sanbornite-quartz gneissic metamorphic rock, especially where the quartz content is high. In small veins of pyrometamorphic rankinite paralava within gehlenite hornfelses (Israel).
It is found associated with Sanbornite, quartz, wollastonite, celsian, taramellite, pyrrhotite, pyrite, witherite, fresnoite. Zadovite, gurimite, rankinite, gehlenite, garnet (Israel).
The name refers to Robert E. Walstrom, mineral collector of Fresno, California, USA, who first recognized the distinctive character of the mineral.