jade, jadeite, fei cui, Japan, gems

Peculiar stone characterized by interlaced structure, tenacious feeling and beautiful grass green color, similar to nephrite jade was found in 1966 in Chisaka area, Hidaka Province, central Hokkaido. This stone has been called Hidaka Jade" after the locality name. The stone consists mainly of chrome-diopside, associated with small amount of uvarovite, chromite and pectolite. The stone is formed as network veins cutting through the boundary between serpentinite and rodingite, both of which intruded into the Jurassic formations in the Kamuikotan structural belt, central axial zone of Hokkaido. In some parts of rodingite, fine veins consisting of grossularite and kammererite are found. It is observed sometimes that kammererite is replaced by chrome-diopside retaining the original fibrous structure. For these observations the author led the following conclusions on the genesis of this chrome-diopside jade. In the shear zone along the boundary between the serpentinite and rodingite, ascending hydrothermal solution that passed through the serpentinite including chromite ores dissolved chromium on a way and repeatedly formed some chromian minerals. Chrome-diopside after kammererite retained the original fabric 0L interlaced structure, then became a jade-like precious stone. Therefore, the author proposes to call this precious stone "Chrome-diopside jade" or "Hidaka jade" as a new variety of jade It is noteworthy that the chrome-diopside in question is bigger in cell volume compared with chrome-diopside from Horoman peridotite which is considered to be an Upper Mantle material. Above-stated features and facts may support author's view that "Hidaka jade" might have been formed in situ."