Two rectorite samples, a Na- and Ca-rich rectorite (sample I) from Beatrix Mine, South Africa, and aNa-rich rectorite (sample 2) from Garland County, Arkansas, have been investigated quantitatively by solid-state 23Na, 27 AI, and 29Simagic-angle spinning (MAS) NMR spectroscopy, total chemical dissolution, cation exchange, and X-ray diffraction (XRD). Comparison of modeled and experimental diffractograms shows that both rectorite samples have a mica to smectite ratio of 1:1 and an ideal ordering in units of one mica plus one smectite layer. The average thicknesses of the coherent scattering domains are ten and eight 2:1 layers for samples 1 and 2, respectively. Quantification of the 23Na, 27AI, and 29SiMAS NMR spectra has allowed determination of the compositions for the octahedral sheets and for the mica (paragonite and margarite) and smectite tetrahedral sheets and determination of the distribution ofinterlayer Na+ ions between paragonite and margarite interlayers. Each 2: 1 layer has an octahedral sheet of weak positive charge sandwiched between two tetrahedral sheets of weak and strong negative charge. The top and bottom tetrahedral sheets of the coherent scattering domains have strong negative charges and very high cation-exchange capacities for sample 1 and low negative charges for sample 2. Sample 1 is a three-component mixed layer (margarite, paragonite, and smectite), and sample 2 a two-component mixed layer (paragonite and smectite).