Wildcatite, CaFe3+Te6+O5(OH), the second new tellurate mineral from the Detroit district, Juab County, Utah

Abstract

Wildcatite (IMA2020–019) is a new calcium–iron(III) tellurate discovered at the Wildcat prospect in the Detroit district, Juab County, Utah. Wildcatite may take on a variety of appearances, ranging from transparent orange to brown coatings or masses to earthy, white polycrystalline coatings filling jasperoid fracture surfaces. Coatings of wildcatite are generally less than 0.1 mm thick and may cover up to 5 cm2, while nanoscale crystallites of wildcatite may form translucent red-brown “crystals” up to 0.1 mm. Wildcatite is found associated with gold, calcite, aragonite, native tellurium, manganese oxides, iron oxides, rare clinobisvanite, beyerite, coronadite, the Te oxides paratellurite and tellurite, and the Te oxysalts andymcdonaldite, burckhardtite, carlfriesite, eckhardite, frankhawthorneite, khinite, mcalpineite, tlapallite, and xocolatlite. The strongest powder diffraction lines are [dobsÅ(Iobs)(hkl)]: 3.33(100)(011), 2.60(55)(110), 2.30(59)(111), 2.05(33)(021), and 1.80(88)(112). The average size of wildcatite crystallites is 13 nm, thus the crystal structure of wildcatite was solved by Rietveld refinement, converging to a final RB value of 3.14%. The empirical formula of wildcatite, as determined by electron probe microanalysis and Rietveld refinement, is Ca0.98Bi3+0.02Pb0.01Fe3+0.73Mg0.05Mn2+0.02Zn0.01Cu0.00Te6+1.15Sb5+0.02Si0.01O5.44H0.56, simplified to the ideal formula of CaFe3+Te6+O5(OH). Wildcatite is trigonal, crystallizing in the space group P1m, with a = 5.2003(14) Å, c = 4.9669(14) Å, V = 116.3(1) Å3 and Z = 1. Wildcatite is structurally very similar to rosiaite (PbSb2O6), possessing a honeycomb-like two-dimensional framework of edge-sharing Fe3+O6 and Te6+O6 octahedra, sandwiching octahedrally coordinated Ca2+ cations. Minor OH substitution (∼10%) at the O sites is required for charge balance in wildcatite.