White crystal aggregates of the rare strontium mineral slawsonite from Kagami, Kochi City, Kochi Prefecture, Shikoku Island, Japan. — Photo: David Hospital · CC BY-SA 4.0
Slawsonite
Slawsonite is an IMA-recognized mineral species in the silicate class, with the chemical formula Sr(Al₂Si₂O₈).
It crystallizes in the monoclinic crystal system (space group I2/c).
Key properties: Mohs hardness 5.5–6.5; specific gravity 3.05; White streak; optically biaxial.
IMA symbol Sws, IMA status: approved, named in 1967.
Found in pectolite veinlets in metamorphosed xenoliths (Rendai, Japan); in a xenolith in ultramafic rock (Sarusaka, Japan).
It is found associated with Calcite, phlogopite, albite, pyrite (Wallowa Mountains, Oregon, USA); celsian, cymrite, xonotlite, prehnite, grossular, diopside (Sarusaka, Japan).
The name refers to Professor Chester Baker Slawson (1898–1964), mineralogist at the University of Michigan, Ann Arbor, Michigan, USA.