M. Jaboyedoff et al., An empirical Scherrer equation for weakly swelling mixed-layer minerals, especially illite-smectite, CLAY MINER, 34(4), 1999, pp. 601-617
The Scherrer equation links the measured width of an X-ray diffraction peak
(Scherrer width, SW) to the number of stacked cells (N) in the direction n
ormal to the diffracting planes. The formula is only valid for one d-value
occurring in the coherently diffracting domain. This equation can be modifi
ed for weakly swelling mixed-layer minerals. This assumes that the peak bro
adening caused by the mixed-layering is proportional to the amount of swell
ing component (S) and that the effects of size and mixed-layering are addit
ive.
If two SW can be measured on XRD patterns from samples treated in two diffe
rent ways (such as air dried or glycolated), N and S can be determined. Thi
s equation is applicable to illite-smectite mixed-layer minerals with high
illitic content. The results are most accurate for N>30. The use of Scherre
r's equation is discussed.