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

Liberto de Pablo-Galan1 and M. L. Chávez-García2
1 Instituto de Geología, Universidad Nacional Autonoma de México, Ciudad Universitaria, 04510 México, D.F.
2 Facultad de Química, Universidad Nacional A. de México, Ciudad Universitaria, 04510 México, D.F.

Abstract: Dioctahedral 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:

(Si13.77Al2.23)Al8O40(OH)8·Ca0.39Na0.03K1.06·(Al3.79Fe+30.09Fe+20.06Mg0.26)(OH)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.

Key Words: Chlorite-smectite clay • Clays • Di,tosudite • Mexico • Mixed-layer clay • Tosudite

Clays and Clay Minerals; April 1994 v. 42; no. 2; p. 114-122; DOI: 10.1346/CCMN.1994.0420202
© 1994, The Clay Minerals Society
Clay Minerals Society (www.clays.org)