Structural and chemical characterization of kaolinite from the Capula clay in Michoacán region, Mexico, by X-ray diffraction and electron microscopy

The traditional ceramic industry, one of the oldest in the world, is based on the use of natural clays, whose mineralogical composition and crystalline structure govern their properties and applications. This study characterized the structural and chemical properties of the clay mineral obtained from the clay collected in Capula, Michoacán, México, a community renowned for its pottery tradition. The sample was prepared through sieving and gravity separation and characterized using X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). SEM images revealed a flake-like laminar morphology with layered growth, while EDS analysis indicated a homogeneous distribution of aluminum (Al), silicon (Si), and iron (Fe). Together with the XRD results, these findings identified the dominant clay mineral as an iron-rich triclinic kaolinite, with lattice parameters be a = 5.21 Å, b = 8.80 Å, and c = 7.51 Å, with angles α = 92.24°, β = 105.01°, and γ = 90.43°, and it was assigned to the space group P 1. Nanoscale structural analysis using TEM and high-resolution TEM (HRTEM) revealed forbidden reflections in the electron diffraction patterns, attributed to double diffraction effects. The VESTA and SimulaTEM simulations showed excellent agreement with the experimental images, confirming the structural identification.