Abstract:
A new mineral avdoninite has been found together with euchlorite, paratacamite, atacamite, belloite and lan-gbeinite among exhalation sediments of the fumarole «Yadovitaya» at the Second Cinder Cone at the Northern Break of the Large Fissure Tolbachik Eruption, Tolbachik volcano, Kamchatka Peninsula, Russia. Avdoninite forms imperfect, short-prismatic, partly flattened crystals up to 0.2 mm in length, with observed forms (001) and (100), their aggregates and (together with atacamite) pseudomorphs after melanothallite. The mineral is brittle, Mohs' hardness 3 (for aggregates). DmcK = 3.03(3) g/cm3; Dcaic = 3.066 g/cm3. Biaxial (optically neutral), a 1.669(2), P 1.688(2), у 1.707(5); 2V= -90°. Dispersion is not observed. Orientation: Y= с, Х= Ы Pleochroism is absent. IR spectrum suggests the presence of water molecules in avdoninite. Chemical composition (electron microprobe, wt. %): K20 11.94 (±0.4), CuO 51.43 (±0.7), CI 37.07 (±0.6), H20 (determined by the Penfield method) 6.9, -0=C12 -8.37; total sum 98.97%. The empirical formula of avdoninite: Ki^CusooClgos (OH)3 87 1.03H2O. Avdoninite is monoclinic, space group P2/m, P2 or Pm; a = 24.34 (2) A, b = 5.878(4) A, с = 11.626 (5) A, P = 93.3 (1)°, V= 1660.6 (20) A3; Z = 4. Compatibility is good: 1 - KJK,. = 0.056 for £>Ыс; 1 - Kp/Kc = 0.044 для A™»»- The strongest lines of the powder difraction pattern [d, A (/, %) (AW)] arc: 11.63 (100) (001), 5.88 (20) (010), 5.80 (27) (002), 5.73 (17) (102), 2.518 (19) (214), 2.321 (17) (005). The new mineral is identical to the previousely described technogenetic analogue of avdoninite from Blyava pyrite deposit, (Orenburg region, Russia). It is named after Vladimir Nikolaevich Avdonin (b. 1925), senior researcher of the Geological Museum of the Urals State Mining Academy. The holotype specimen of avdoninite from Kamchatka is deposited in the Mineralogical Museum of Department of Mineralogy of the St. Petersburg State University (inventory N 19175).