Sample preparation effects on illite crystallinity measurement: grain‐size gradation and particle orientation

Publisher Website
Google Scholar
Abstract
Specimen thickness is the main experimental factor controlling the results of illite crystallinity (IC) or crystallite size measurements on sedimentation slides. Different values obtained from thick and thin preparations are due to grain‐size gradation effects, which may exclude larger and higher ordered grains from contributing to the diffraction. Orientation effects control the measured peak intensity. The change from poor particle orientation in thick slides to high orientation in very thin slides is marked by an increase in specimen density, diminishing non‐basal reflections, and by a strong increase in peak intensity. A plateau with constant peak breadths is observed if thin slides of well ordered, platy illites are used. A similar plateau can be recognized for thick preparations of specimens from less ordered materials, but not from well ordered ones. Therefore, it is suggested that IC is determined on very thin sedimentation slides with a thickness of 0.25 mg/cm2 or less. Ultrasonic and H2O2 treatments enhance the degree of particle orientation by destruction of grain aggregates and organic compounds, leading to smaller peak breadths and higher intensities.