Haitaite‐(La), LaU4+Fe3+2(Ti13Fe2+4Fe3+)Σ18O38, a New Member of the Crichtonite Group

Abstract

AbstractHaitaite‐(La), (La, Ce)(U4+, U6+, Fe2+)(Fe3+, Al)2(Ti, Fe2+, Fe3+)18O38, is a new member of the crichtonite group. It is named after the Haita Village in the Miyi County of Sichuan Province, China, where the mineral was discovered. The mineral occurs as black opaque centimeter‐sized aggregates in the external contact zone between the Neoproterozoic (∼800 Ma) alkali feldspar granite and the Mesoproterozoic (∼1700 Ma) micaschist. In the studied sample, haitaite‐(La) is associated with other minerals, including ilmenite, magnetite, rutile, zircon, brannerite and uraninite. The new mineral is a black, metallic phase and has a Mohs hardness of 6, with a density of 4.99 g/cm3 (calculated) and 5.03 g/cm3 (measured). Haitaite‐(La) is opaque in transmitted light and grayish‐white under reflected light, with a reflectivity between 22.5% and 16.42% in the 400–700 nm band (SiC, in the air). The compositions of the mineral were measured by EPMA, the U4+/U6+ ratio was determined by X‐ray photoelectron spectroscopy and the Fe2+/Fe3+ ratio was determined by Mössbauer spectroscopy. Haitaite‐(La) is trigonal, belongs to and has unit‐cell parameters a = 10.3678(5) Å, c = 20.8390(11) Å, V = 1939.9(2) Å3, Z = 3. The crystalline structure is composed of octahedra with 9 layers of close‐packed octahedra (M1, M3, M4, M5), tetrahedra (M2) and contains large 12‐coordinated M0 sites.