Noncrystalline Fe-Si-Al-Oxyhydroxides

Richard A. Eggleton
Department of Geology, Australian National University, Canberra, ACT 2600, Australia

Abstract: High-resolution transmission electron microscopy of noncrystalline Fe-Si-Al-oxyhydroxide gels shows a common structure of hollow packed spheres having external diameters ranging from 50 to 1000 Å. Some sphere walls display a concentric structure, particularly if the gel composition is close to that of a crystalline clay mineral (e.g., smectite, kaolin). The spheres probably formed by expansion of void space (bubbles) as the surrounding gel contracted 5–10% because of partial ordering of the Fe-Si-Al-oxygen network. Much of the water contained in such noncrystalline minerals is incorporated within the bubbles.

Key Words: Gels • High-resolution transmission electron microscopy • Iron • Morphology • Noncrystalline oxyhydroxides

Clays and Clay Minerals; February 1987 v. 35; no. 1; p. 29-37; DOI: 10.1346/CCMN.1987.0350104
© 1987, The Clay Minerals Society
Clay Minerals Society (www.clays.org)