Sanguite, KCuCl₃, a New Mineral from the Tolbachik Volcano, Kamchatka, Russia

A new mineral sanguite, KCuCl₃, is found in the Glavnaya Tenoritovaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. Associated minerals are belloite, avdoninite, eriochalcite, sylvite, halite, carnallite, mitscherlichite, chrysothallite, romanorlovite, mellizinkalite, gypsum, chlorothionite, kainite, sellaite, and earlier hematite, tenorite, and chalcocyanite. Sanguite forms prismatic crystals up to 1 mm long and up to 0.2 mm thick, typically combined in groups, dense clusters, or crusts up to several dozens of cm² in area. The major crystal forms are {011}, {100}, and {010}. The mineral is transparent, with vitreous luster. Its color is bright red, and slightly altered samples are dark red to brownish red. Sanguite is brittle. Its Mohs' hardness is ca 3. Cleavage is perfect on (010), fracture is stepped. D_meas = 2.86(1), D_calc = 2.88 g cm⁻³. Sanguite is optically biaxial (−), α 1.653(3), β 1.780(6), γ 1.900(8), 2V_meas = 85(5)°. The Raman spectrum is reported. The chemical composition (wt.%, electron microprobe data) is: K 18.57, Cu 29.79, Cl 50.66, total 99.02. The empirical formula calculated on the sum of atoms = 5 pfu is: K_1.00Cu_0.99Cl_3.01. Sanguite is monoclinic, P2₁/c, a 4.0281(2), b 13.7906(5), c 8.7335(4) Å, β 97.137(4)°, V 481.38(3) ų, and Z = 4. The strongest reflections of the powder X-ray diffraction pattern [d, Å(I)(hkl)] are: 7.36(78)(011), 6.92(100)(020), 3.684(69)(111), 3.146(64)(032, 102), 3.068(63)(112), 2.857(73)(122), 2.709(82)(112, 042), and 2.574(56)(122). The crystal structure, solved from single-crystal X-ray diffraction data (R = 0.0545), contains almost planar, discrete dimers [Cu²⁺₂Cl₆]. The KCl₉ polyhedra are connected via common faces to form interrupted layers. Neighboring layers are linked to each other by the common edges of the K-centered polyhedra. The mineral is named from the Latin sanguis (blood), alluding to its color.