Cadmoindite, a new mineral, has been found around a high-temperature fumarole's vent on Kudriavy volcano, Iturup isle, Kurily, Russia. Octahedron crystals of cadmoindite up to 0.15 mm in size occur in close association with isometric grains of pyrite and translucent hexagonal platy crystals of Cd-bearing wurtzite, forming dry aggeregates as well as groups of individual isolated crystals on the surface of cracks in fumarole's crust at temperature about 450-600 deg C. Samples with cadmoindite contain also platy crystals of rhenium disulfide (rheniite), greenockite and needles of Pb-Bi sulfosalts (possibly, lillianite). Most crystals of cadmoindite have triangle-shaped step growth patterns on the sides of crystals. Mineral has black to dark brown color and adamantine luster; streak is brown. Under reflected light cadmoindite is gray with distinct brown-red internal reflections. The measured microhardness VHN_(20) is 206. Electron microprobe analyses gave: Cd 19.98, Fe 1.71, Zn 0.77, In 49.51, Ge 0.29, S 27.53, Se 0.04, sum 99.83 wt percent. The empirical formula, calculated on 7 atoms is (Cd_(0.82)Fe_(0.14)Zn_(0.05))_(1.01) (In_(1.99)Ge_(0.02))_(2.01)S_(3.98). Idealized formula is CdIn_2S_4. The strongest nine lines of powder diffraction pattern [d in A (I) (hkl)] are: 3.87(4) (002), 3.27(10) (113), 2.70(6) (004), 2.07(8) (115, 333), 1.91(9) (044), 1.41(6) (137, 355), 1.246(7) (157, 555), 1.107(9) (484), 1.045(8) (159, 377). Cubic symmetry group. The unit cell parameter of cadmoindite a= 10.81 +- 0.02 A; V= 1263.21 A~3, Z - 8, space group Fd3m. X-ray analysis of cadmoindite shows that this mineral is an analogue of synthetic compound CdIn_2S_4 with the spinel type of structure. The mineral is named after its chemical composition. Type material is deposited in Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow.
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