Randomly Interstratified Serpentine/Chlorite: Its Detection and Quantification by Powder X-ray Diffraction Methods

Abstract

X-ray diffraction studies of the pore-lining chloritic mineral from the Tuscaloosa Formation disclose a marked pattern of odd-order line broadening for the 001 to the 00,16 reflections. The odd-order peaks are approximately twice as broad as the even orders after correction for instrumental broadening effects. These results are consistent with a randomly interstratified 7-Å/14-Å structure, which is most likely serpentine/chlorite. Quantitative analysis of line broadening and model calculations indicate that the serpentine/chlorite contains 7% serpentine layers.

A simplified method is proposed for quantifying randomly interstratified serpentine/chlorite. Residual line broadening (β_r) is obtained from the half-height widths of uncorrected diffraction profiles for the 004 and 005 “chlorite” reflections by means of the following: $\beta_{r}=(\beta_{005}^{1.25}-\beta_{004}^{1.25})^\frac{1}{1.25}.$. Percent serpentine in the random interstratification is computed from the empirical expression $\%S=-0.51+24.27\beta_{r},$ which is valid from about 1 to 20 percent serpentine.