Masutomilite
Tanakami-Mori village, Otsu city, Shiga pref., Japan
Height: 20 mm. Mustomilite exhibiting periodic zoning structure with zinnwaldite. The translucent pale purple beds are mustomilite. The dark brown beds between maustomilite beds and the dark brown part at the lower right are zinnwaldite. The photograph is parallel to cleavage along the (001) basal plane.
Recovered from an REE Miarolitic pegmatite in S-type (Ilumenite-series) granite. Formed in the Late Cretaceous (70 Ma).
The first masutomilite in the world was described from this location in 1974.