Crystallographic images processing (CIP) and high-resolution transmission electron microscopy (HRTEM) studies of bannisterite; a 2:1 type modulated layer silicate

Two-dimensional CIP was performed on a HRTEM image of bannisterite from Broken Hill, Australia. Bannisterite is monoclinic and crystallizes in space group A2/a with a 2.29, b 1.64, c 2.46 nm, beta 94.36 degrees . Using digitized HRTEM images processed on a personal computer, crystallographic data were extracted from calculated Fourier transforms and processed to give an improved density map of the HRTEM image of bannisterite. Gross features as well as details such as pinching and swelling of the sinusoidal octahedral sheet, overlapping regular and inverted tetrahedra, and the column of large interlayer cations were easily discerned.