Kôzulite, an Mn-rich alkali amphibole

Abstract

The crystal structure of kôzulite, an Mn-rich alkali amphibole with the ideal formula NaNa2[Mn4 2+(Fe3+,Al)]Si8O22(OH)2, tris­odium tetra­manganese iron/aluminium octa­silicate dihydroxide, was refined from a natural specimen with composition (K0.20Na0.80)(Na1.60Ca0.18Mn2+ 0.22)(Mn2+ 2.14Mn3+ 0.25Mg2.20Fe3+ 0.27Al0.14)(Si7.92Al0.06Ti0.02)O22[(OH)1.86F0.14]. The site occupancies determined from the refinements are M1 = 0.453 (1) Mn + 0.547 (1) Mg, M2 = 0.766 (1) Mn + 0.234 (1) Mg, and M3 = 0.257 (1) Mn + 0.743 (1) Mg, where Mn and Mg represent (Mn+Fe) and (Mg+Al), respectively. The average M—O bond lengths are 2.064 (1), 2.139 (1), and 2.060 (1) Å for the M1, M2, and M3 sites, respectively, indicating the preference of large Mn2+ for the M2 site. Four partially occupied amphibole A sites were revealed from the refinement, with A(m) = 0.101 (4) K, A(m)′ = 0.187 (14) Na, A(2) = 0.073 (6) Na, and A(1) = 0.056 (18) Na, in accord with the result derived from microprobe analysis (0.20 K + 0.80 Na), considering experimental uncertainties.

Mangani-eckermannite, NaNa2(Mg4Mn3+)Si8O22(OH)2, a new amphibole from Tanohata Mine, Iwate Prefecture, Japan

“…It should be also noted that the data reported by Barkley et al (2010) show very close Mg and Mn 2+ values (2.20 vs. 2.14 apfu) as well as Fe 3+ and Mn 3+ values (0.27 vs. 0.25 apfu). This means that their sample might contain local compositions corresponding to different amphibole species including the mangani-eckermannite described here.…”

“…The official IMA-CNMNC List of Mineral Names (Pasero, 2023, http://cnmnc. main.jp/) includes mangano-ferri-eckermannite as a valid mineral species referring to Barkley et al (2010) and Hawthorne et al (2012). However, the empirical chemical formula was reported by Barkley et al (2010) 2+ and Fe 3+ > Mn 3+ > Al as C-cations and, thus, formally corresponds to magnesio-arfvedsonite but not mangano-ferri-eckermannite.…”

“…main.jp/) includes mangano-ferri-eckermannite as a valid mineral species referring to Barkley et al (2010) and Hawthorne et al (2012). However, the empirical chemical formula was reported by Barkley et al (2010) 2+ and Fe 3+ > Mn 3+ > Al as C-cations and, thus, formally corresponds to magnesio-arfvedsonite but not mangano-ferri-eckermannite. This questions the existence of mangano-ferri-eckermannite as a valid mineral species (although, it can exist as a so-called 'named amphibole'), at least, as applied to the sample studied by Barkley et al (2010).…”

“…Kitamura and Morimoto (1972) presented the structure refinement of a kôzulite crystal with the composition (Na 2.54 K 0.27 Ca 0.19 )(Mn 3.69 Mg 0.63 Fe 3+ 0.33 Al 0.31 )Si 8.00 O 21.789 [(OH) 2.18 F 0.04 ], however, they did not report detailed structure information, such as atomic coordinates and displacement parameters, as well as the valence of Mn. Later, Barkley et al (2010) refined the structure of kôzulite giving the ideal formula as NaNa 2 [Mn 2+ 4 (Fe 3+ ,Al)]Si 8 O 22 (OH) 2 . After the adoption of the current amphiboles nomenclature (Hawthorne et al , 2012), kôzulite was redefined to mangano-ferri-eckermannite (see, e.g.…”

“…The official IMA-CNMNC List of Mineral Names (Pasero, 2023, ) includes mangano-ferri-eckermannite as a valid mineral species referring to Barkley et al (2010) and Hawthorne et al (2012). However, the empirical chemical formula was reported by Barkley et al (2010) as (K 0.20 Na 0.80 ) Σ1.00 (Na 1.60 Ca 0.18 Mn 2+ 0.22 ) Σ2.00 (Mn 2+ 2.14 Mn 3+ 0.25 Mg 2.20 Fe 3+ 0.27 Al 0.14 ) Σ5.00 (Si 7.92 Al 0.06 Ti 0.02 ) Σ8.00 O 22 [(OH) 1.86 F 0.14 ] Σ2.00 , i.e. it has Mg > Mn 2+ and Fe 3+ > Mn 3+ > Al as C-cations and, thus, formally corresponds to magnesio-arfvedsonite but not mangano-ferri-eckermannite.…”