Structural investigations of sudoite and regularly interstratified sericite/sudoite

Abstract

The z parameters of atomic planes in two sudoites and one regularly interstratified sericite/sudoite from Kuroko deposits have been refined using 00l X-ray reflections. The results indicate that the interlayer O–OH space is similar to, but the dioctahedral 2 : 1 layer thickness is thinner than in trioctahedral chlorites. The octahedral cation number in the interlayer sheet is a little less than 3.0 atoms. A structural formula [Mg_1.3Al_1.5(OH)₆]^1.1+[(Mg_0.3Al_1.7)(Si_3.2Al_0.8)O₁₀(OH)₂]^1.1− is suggested for the sudoite from the X-ray, chemical, and thermogravimetric data. The fit of the dioctahedral and trioctahedral sheets seems to be explained by the chemical composition of the two sheets.
The interstratified sericite/sudoite gives hkl reflections, which have been indexed in terms of an orthohexagonal cell (b=9.02₄, c=24.14Å). A stacking sequence composed of 1 M or 2 M₁ mica and IIb chlorite layer types has been found on the basis of the 20l intensities.