Ehrigite, Bi8Te3, a New Member of the Tetradymite Group

Abstract Ehrigite, Bi8Te3, is a new member of the tetradymite group and crystallizes in the trigonal crystal system (space group: , #166). Its cell dimensions are a = 4.519(6) Å, c = 65.182(24) Å, Z = 3, and V = 1152.771(7.554) Å3. Ehrigite occurs as sub-100-micron-sized grains in hedenbergite skarn from the abandoned Good Hope gold mine, Hedley district, British Columbia, Canada. The mineral and name have been approved by the IMA Commission on New Minerals and Mineral Nomenclature (proposal 2023-074). Ehrigite is compositionally and structurally distinct from hedleyite, Bi7Te3, with which it coexists. Ehrigite is opaque, with a pale gray color in reflected light. Reflectance is higher than tetradymite and slightly higher than hedleyite. It appears gray against native bismuth. The ehrigite structure consists of a single 11-atom layer visualized in atomic-scale high-angle annular dark field scanning transmission electron microscope images and further constrained from ab initio total energy calculations and structure relaxation using density functional theory using the measured parameters as input data. Scanning transmission electron microscope simulations also closely match the crystal structure model and images. Phases of the tetradymite and related modular mineral groups are well suited to visualization, indexing, and diffraction using a high-angle annular dark field scanning transmission electron microscope. The addition of density functional theory methodology to corroborate and refine structural characteristics provides a valuable approach for understanding these complex yet predictable minerals.