Andymcdonaldite is a new ferric-iron-tellurate mineral that occurs within Au-, Te-, and Bi-rich jasperoid at the Wildcat prospect in the Detroit district, Juab County, Utah. The mineral has a yellow-brown to brownish-black color, occurs as extremely cryptocrystalline (11–25 nm) material in thin films and breccia matrix fillings, and is associated with gold (native), tellurium (native), beyerite, clinobisvanite, and a variety of tellurium oxysalt minerals that include carlfriesite, eckhardite, frankhawthorneite, khinite, mcalpineite, paratellurite, tellurite, tlapallite, and xocolatlite. This is the first known natural occurrence of a phase with an ordered (tetragonal) inverse trirutile structure (A3+2B6+O6) which has many synthetic representatives. The B site in andymcdonaldite is occupied by Te and the A site is dominated by Fe with up to approximately 14 mole% substitution by other cations. An empirical formula of (Fe1.74Cu0.12Mn0.06Al0.05Mg0.05)Σ2.02Te1.01O6 was obtained from electron microprobe analyses.
Powder X-ray diffraction data, Raman spectra, and unit-cell dimensions for andymcdonaldite strongly resemble those for the synthetic analogue, Fe3+2Te6+O6. The strongest X-ray diffraction lines are [dobsÅ(Iobs)(hkl)]: 4.14(27)(101), 3.28(100)(110), 2.54(71)(103), 1.71(72)(213), and 1.37(39)(303,116). The strongest Raman bands are at 748, 643, and 417 cm–1. The space group is P42/mnm and the cell dimensions are a 4.622–4.630 Å, c 9.077–9.087 Å, and V = 193.94–194.80 Å3 (Z = 2).