New X‐ray rietveld refinement of kaolinite from Keokuk, Iowa

The positions of 13 non‐hydrogen atoms in the structure of kaolinite from Keokuk, Iowa, were refined in the space group C1 using the constrained X‐ray Rietveld refinement. The precision and accuracy of the atomic positions are better than those previously reported. The most frequent e.s.d.'s of the positional parameters range from 0.003 to 0.005; the SiO bond distances are from the interval 1.56(4)–1.68(3) Å, and the AlO from 1.80 (5) to 2.07 (5) Å. The ditrigonalization angle α characteristic for tetrahedral sheet was found to be 9°, this value is in good agreement with the 11° reported from single crystal data. The correction for preferred orientation was in the form of exp (G cos (2α)), the final factors of agreement were Rwp = 23.1%, RF = 9.2% and S = 1.4.