Abstract
A new, unusual Fe-free and As5+-enriched variety of chladniite, a rare phosphate of the fillowite group was found in exhalations of the active Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. It belongs to the high-temperature (500–750°С) paragenesis with calciojohillerite, fluorapatite, metathénardite, diopside, enstatite, forsterite and hematite. This genetic type is novel for fillowite-group minerals. The crystal structure of Tolbachik chladniite is solved, R1 = 4.32%. It is trigonal, R–3, a = 14.9831(2), c = 42.8050(7) Å, V = 8322.1(3) Å3. The structural formula is: M13(Na0.56\(\square \)0.44)\(_{2}^{{M21}}\)(Na0.81Ca0.19)\(_{2}^{{M31}}\) (Na0.97\(\square \)0.03)\(_{6}^{{M12}}\)(Ca0.64Na0.36)\(_{6}^{{M1}}\)MnM2(Mg0.54Ca0.46)M3–9Mg\(_{{30}}^{{M10}}\)(Mg0.94Ca0.06)\(_{6}^{{M11}}\)Mg6(P33.53As2.47)O144 (Z = 3). The crystal chemical features of chladniite and their correlation with mode of occurrence are discussed for all chladniite findings known in meteorites and terrestrial objects of different genetic types.
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