The behaviour of Mn in amphiboles; Mn in synthetic fluor-edenite and synthetic fluor-pargasite

The crystal structures of two synthetic C2/m amphiboles, manganoan fluor-edenite Na (sub 1.06) (Ca (sub 1.41) Na (sub 0.12) Mn (sub 0.47) )(Mg (sub 4.44) Mn (sub 0.41) Al (sub 0.15) )(Si (sub 6.91) Al (sub 1.09) )O (sub 22) F (sub 2) , with a 9.829, b 18.024, c 5.284 Aa, beta 104.66 degrees , and manganoan fluor-pargasite (Na (sub 0.96) Ca (sub 0.13) )(Ca (sub 1.51) Mn (sub 0.40) )(Mg (sub 3.47) Mn (sub 0.73) Al (sub 0.80) )(Si (sub 5.95) Al (sub 2.05) )O (sub 22) F (sub 2) , with a 9.812, b 17.926, c 5.308 Aa, beta 105.10 degrees have been refined to R 2.0 and 1.4%, respectively. Site-scattering and EPMA data both indicate that there is a large amount ( approximately 0.50 pfu) of Mn (super 2+) at the M4 site in both these synthetic amphiboles. C-group Mn (super 2+) shows the ordering pattern M2 >><$I>>><$I> M1 >><$I>>><$I> M3 in these amphiboles; this is a significantly different behaviour from that of Fe (super 2+) which shows the ordering pattern M1 up to M3 in Mn-poor calcic, sodic-calcic and alkali amphiboles. The presence of significant Ca at the A site in F-rich pargasite is also confirmed.