• journal_title：American Mineralogist
• Contributor：Fernando Scordari ; Emanuela Schingaro ; Ernesto Mesto ; Maria Lacalamita
• Publisher：Mineralogical Society of America
• Date：2012-11-01
• Format：text/html
• Language：en
• Identifier：10.2138/am.2012.4262
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：97
• issue：11-12
• firstpage：2016
• section：Articles

The 2M₁-phlogopite from the potassic gabbronorite (Black Hill, Australia) has been studied by electron microprobe and single-crystal X-ray diffraction analyses. The crystal-chemical formula was (K_0.95Na_0.01)(Al_0.15Mg_1.27Fe²⁺_1.16Fe³⁺_0.04Ti⁴⁺_0.38)(Si_2.85Al_1.15)O_10.76F_0.11Cl_0.03OH_1.10. The structural analysis has shown that the crystal has the cell parameters a = 5.352(1), b = 9.268(1), c = 20.168(1) Å, and β = 95.10(1)° and exhibits symmetry lowering from the ideal space group C2/c to C1. An octahedral cation ordering pattern was revealed from the refined site-scattering powers. Specifically, using the scattering species Mg vs. Fe, it was found that the M1 site at z = 0 was occupied principally by Mg (~77%) and subordinately by Fe (~23%), whereas that at z = 0.5 was completely occupied by Fe; the M2 sites at z = 0 displayed ~88% Mg and ~12% Fe, whereas those at z = 0.5 were occupied by ~86% Fe and ~14% Mg. The analysis of geometrical features shows that the Ti uptake in the structure via the Ti-oxy mechanism induces structural distortions of different extents on the z = 0 and z = 0.5 layers, with stronger effects for the layer at z = 0. Minor chemical and structural differences, instead, affect the T sheets at z = 0 and z = 0.5.