Abstract
A jadeite rock from Oosa-cho, northern part of Okayama, is associated with serpentinite of the Sangun metamorphic belt. It consists predominantly of jadeite with such accessary minerals as grossular, analcime, prehnite, vesuvianite, natrolite, thomsonite, stronalsite, zircon, deweylite, chlorite and diopside. It is cut by many veinlets composed of one or more of grossular, analcime, vesuvianite, stronalsite, chlorite and zeolite minerals.
On the electron microprobe image, some of jadeite crystals show a growth zoning of diopsidic (Jd96Di3Fs1) and pure (approximately Jd100) parts. Some crystals of garnet show chemical zoning. The core is poor in TiO2, FeO and CaO, but rich in Al2O3 as compared with the rim. Zircon occurs sporadically. Under the microscope, a few grains of stronalsite are observed. Its chemical composition is very similar to the ideal formula, Na2SrAl4Si4016. Ba-rich parts are also recognized in a stronalsite crystal.
