Kenomicrolite, □₂Ta₂O₄(OH)₂□, the first vacancy-dominated pyrochlore-supergroup mineral from the Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil

Kenomicrolite (IMA 2024-097), ideally Ta[O(OH)], is a newly approved mineral species from the Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil.It is the first member of the pyrochlore supergroup to exhibit dominant vacancies at both A and Y sites and a Ta-dominated B site, making it a tantalum oxyhydroxide.It occurs as an accessory mineral within a microlite group assemblage, probably of secondary origin via weathering-induced leaching and hydration of fluorcalciomicrolite. Kenomicrolite appears as pale orange, transparent, isotropic octahedral crystals up to 200 m in size, with a calculated density of 5.599 gcm and calculated refractive index of experiments in Tl + -rich solutions showed minimal incorporation (~0.19 Tl + pfu), highlighting limited ion-exchange capacity due to vacancy-dominated tunnel sites.The structural stability and low hydration make kenomicrolite an important endmember for understanding vacancy-rich pyrochlore systems and their constraints on ion incorporation mechanisms.