Dioctahedral Tosudite in Hydrothermally Altered Pliocene Rhyolitic Tuff, Neutla, Mexico

Abstract

AbstractDioctahedral tosudite, a regular interstratification of dioctahedral chlorite-dioctahedral smectite, occurs associated with kaolin in the hydrothermal area of Delgado, Neutla, Mexico. Its composition corresponds to the formula: $$\left( {S{I_{13.77}}A{L_{2.23}}} \right)A{L_8}{O_{40}}{\left( {OH} \right)_8} \cdot C{A_{0.39}}N{A_{0.03}}{K_{1.06}} \cdot \left( {A{L_{3.79}}F{E^{ + 3}}_{0.09}F{E^{ + 2}}_{0.06}M{G_{0.26}}} \right){\left( {OH} \right)_{12}}.$$ It forms as thin irregular flakes up to 5 µm in size. Adsorbed and cation hydration interlayer H2O is lost at 81°C and 184°C, dehydroxylation is intense at 496°C and weak at 656°C, with recrystallization at 970°C and 989°C. Infrared analysis shows OH-stretching at 3605 cm-1 assigned to the Al-OH-Al group and at 3628, 3500, and 3365 cm-1. Also, OH-bending occurs at 822 cm-1, deformation of the H2O molecule at 1630 cm-1, Si-O stretching at 1020 cm-1, and bending at 482 cm-1, displaced by Al substitution and increase of the Si-O distance. The characteristic basal spacing of 29.49 Å for the air-dry mineral is changed to 31.32 Å when solvated and to 23.23 Å upon heating; d060 = 1.496 Å. The interstratification is a regular 1:1 dioctahedral chlorite-dioctahedral smectite, R = 1, with coefficient of variability 0.73% for the air-dried mineral and 0.76% for the solvated one.