Oxyyttrobetafite–(Y), Y2Ti2O6O, a new mineral of the pyrochlore supergroup in a pegmatite from Souri Valley, Komono, Mie Prefecture Japan

Oxyyttrobeta fi te – (Y) is the fi rst member in the beta fi te group of the pyrochlore supergroup found in albite – rich pegmatite from Souri Valley, Komono, Mie Prefecture, Japan. This new mineral occurs as small anhedral grains with sizes of 20 to 200 µm in cylinder – shaped aggregates with a substrate of thalénite – (Y) and synchysite – (Y). Small amounts of aeschynite – (Y), thorianite, and thorite are also associated in the same occurrence with oxyyttrobeta fi te – (Y), and gadolinite – (Y) is also included at the boundary between the aggregate and albite. The physical properties are: brown in color, brittle, transparent, non – fl uorescent, vitreous luster, white streak with a Mohs hardness of 5, and a calculated density of 5.54 g·cm − 3 . Oxyyttrobeta fi te – (Y) is an optically isometric material with brown color under the microscope with a refractive index of n = 2.3 calculated using the Gladstone – Dale relationship. The empirical formula of oxyyttrobeta fi te – (Y) calculated on the basis of B = 2 with A 2 B 2 X 6 Y composition is (Y 1.58 Dy