Chemical and structural characterization of henryite, (Cu,Ag)3+xTe2 (x ≈ 0.40): A new structure type in the (Ag)–Cu–Te system

• The structure of natural henryite has been solved for the first time.
• A new structure type is reported in the (Ag)–Cu–Te system.
• Non-stoichiometry could cause disorder phenomena during the crystal growth.

The crystal structure of the mineral henryite, a rare copper–silver telluride, was solved using intensity data collected using a crystal from the type locality, the Campbell orebody, Bisbee, Arizona (U.S.A.). The study revealed that the structure is cubic, space group Fd  3¯c, with cell parameters: a = 12.1987(5) Å, and V = 1815.3(2) Å3. The refinement of an anisotropic model led to an R index of 0.0301 for 168 independent reflections. The structure consists of a face-centered cubic close-packing of Te atoms with a disordered distribution of Cu and Ag atoms in the partially-occupied tetrahedral interstices. It represents a new structure type in the Cu–Te system closely resembling the cubic structure of the well known phase A. Electron microprobe analyses of the crystal used for the structural study led to the formula (Cu1.91Ag1.47Fe0.02)Σ=3.40Te2, on the basis of 2 Te atoms per formula unit. On the basis of information gained from the structural and chemical characterization, the crystal-chemical formula was revised yielding (Cu,Ag)3+xTe2 (Z = 16) with x ≈ 0.40 instead of [Cu3.77Ag3.01Te4] (Z = 8) as previously reported.

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