Formula: Sr(Al2Si2O8)
Tectosilicate (framework silicate), feldspar group
Specific gravity: 3.05 to 3.5
Hardness: 5½ to 6½
Streak: White
Colour: Colourless, grey
Luminescence: Japan material fluoresces pink to purplish red in short wave UV (AM 72.225-226)
Common impurities: Ti,Fe,Mg,Na,K,H2O

Metamorphic environments


At the Tanaka Olivine Mining Co. quarry, Rendai, Kochi City, Kochi Prefecture, Japan, slawsonite occurs as veinlets cutting pectolite veinlets, which are developed in metamorphosed xenoliths (AM 72.225-226).

At Sarusaka, Konan City, Kochi Prefecture, Japan, in thin sections, colourless, untwinned slawsonite is commonly observed with numerous small crystal inclusions of celsian and cymrite and sometimes xonotlite, prehnite, grossular, and diopside. Other associated phases include hydrogrossular, vesuvianite, tobermorite, native copper and calcite (AM 72.225-226) The minerals occur in veinlets cutting a rodingite xenolith in chloritised serpentine (Dana).

At the type locality, the Martin Bridge formation, Wallowa county, Oregon, USA, slawsonite occurs in pectolite veinlets in metamorphosed xenoliths in metamorphosed limestone. Associated minerals include calcite, phlogopite, albite and pyrite (AM 72.225-226, HOM, Webmin, Dana)

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