The crystal structure and redefinition of utahite

Utahite was first described in 1997 based mainly on powder X-ray diffraction data and electron microprobe data. No crystal structure was reported. The re-examination of utahite using single-crystal X-ray diffraction and electron microprobe analysis has shown that utahite contains essential Mg, along with Cu, Zn, Te, O and H. The missing MgO was originally attributed to additional H 2 O. The redefinition of utahite to MgCu 2+ 4 Zn 2 Te 6+ 3 O 14 (OH) 4 ·6H 2 O from Cu 2+ 5 Zn 3 (Te 6+ O 4 ) 4 (OH) 8 ·7H 2 O has been accepted by the IMA–CNMNC, Proposal 20-C. Utahite is triclinic, crystallising in P 1 ¯ with the unit-cell parameters a = 5.6831(4) Å, b = 8.7793(6) Å, c = 9.9818(9) Å, α = 95.415(7)°, β = 104.129(7)°, γ = 90.098(6)° and V = 480.65(7) Å 3 , in good agreement with the original study. Utahite features a new framework arrangement of Cuφ 6 octahedra, Znφ 4 tetrahedra and Teφ 6 octahedra (where φ = O or OH), with Mg(H 2 O) 6 octahedra occupying the channel space. Two-thirds of the Te sites form Te 6 + 2 O 10 dimers and one third form [Te 6+ O 4 (OH) 2 ] 4− octahedra, spatially separated from other Te 6+ sites. Although unique, the structural framework of utahite is similar to that of leisingite, with both minerals having layers composed of Cuφ 6 and Teφ 6 octahedra with Mg(H 2 O) 6 octahedra in the interlayer space; however leisingite does not contain Zn. New Raman spectroscopic data is also reported for utahite.