Maletoyvayamite, Au3Se4Te6, a new mineral from Maletoyvayam deposit, Kamchatka peninsula, Russia

Maletoyvayamite, Au3Se4Te6, is a new mineral discovered in a heavy-mineral concentrate from the Gaching occurrence of the Maletoyvayam deposit, Kamchatka, Russia (60°19′51.87″N, 164°46′25.65″E). It forms anhedral grains (10 to 50 μm in size) and is found in intergrowths with native gold (Au-Ag), Au tellurides (calaverite), unnamed phases (AuSe, Au2TeSe and Au oxide), native tellurium, sulfosalts (tennantite, tetrahedrite, goldfieldite and watanabeite) and supergene tripuhyite. Maletoyvayamite has a good cleavage on {010} and {001}. In plane-polarised light, maletoyvayamite is grey, has strong bireflectance (grey to bluish grey), and strong anisotropy; it exhibits no internal reflections. Reflectance values for maletoyvayamite in air (Rmin,Rmax in %) are: 38.9, 39.1 at 470 nm; 39.3, 39.5 at 546 nm; 39.3, 39.6 at 589 nm; and 39.4, 39.7 at 650 nm. Sixteen electron-microprobe analyses of maletoyvayamite gave an average composition: Au 34.46, Se 16.76, Te 47.23 and S 0.84, total 99.29 wt.%, corresponding to the formula Au2.90(Se3.52S0.44)Σ3.96Te6.14 based on 13 atoms; the average of eleven analyses on synthetic analogue is: Au 34.20, Se 19.68 and Te 45.42, total 99.30 wt.%, corresponding to Au2.90Se4.16Te5.94. The calculated density is 7.98 g/cm3. The mineral is triclinic, space group P1, with a = 8.901(2), b = 9.0451(14), c = 9.265(4) Å, α = 97.66(3), β = 106.70(2), γ = 101.399(14)°, V = 685.9(4) Å3 and Z = 2. The crystal structure of maletoyvayamite represents a unique structure type resembling a molecular structure. There are cube-like [Au6Se8Te12] clusters linked via van der Waals interactions. The structural identity of maletoyvayamite with the synthetic Au3Se4Te6 was confirmed by powder X-ray diffraction and Raman spectroscopy.