The microstructure charateristics of illite from the Chuanlinggou Formation of Changcheng System (Chch) in Jixian County, Tianjin City has been studied by means of high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), X-ray energy dispersive spectrum (EDS) and X-ray powder diffraction (XRD). The Kuebler index of ''illite crystallinity'' is 0.505° Δ2θ, which indicates that the host rock is in a middle diagenetic stage. The chemical analyses of EDS for illite studied indicate a heavily absent in interlayer cation and an average chemical formula of K_(0.57)(AI_(1.80)Mg_(0.42)(Fe^(2+))_(0.12))_(∑=2.34)(Si_(2.92)Al_(1.80))_(∑=4)O_(10)(OH)_2. It is found, from one-dimensional lattice images, that the layers of illite not only stack in a flat way but also in a curving way. A ''matting fabric'' illite structure results from stacking faults. Combined with SAED analysis the illite studied can be affirmed as 1M illite. The two-dimensional lattice images are obtained from [100] and [110] incidences, whose lattice images have the same d-values but different intersecting angles. The two-dimensional lattice image with [100] incidence is orthogonal to each other, whilst that with [110] incidence is oblique. This paper provides some important structure information of authigenic clay minerals for the well-known mesoproterozoic section of Jixian County.
CHEN Tao1,2 & WANG HeJing2? 1 Institute of Gemology, China University of Geosciences, Wuhan 430074, China
