Electron microscopic examination of montmorillonite from the deposit near Redhill shows that the particles of the so-called blue clay are predominantly lathshaped with an average length: width ratio of 5. The so-called yellow clay from Redhill also contains a high proportion of similar lath-shaped particles, but many smaller lamellar particles are present which appear to be the results of lateral fracture of the laths. The majority of particles of montmorillonite in the fullers' earth deposit near Bath, Somerset, are platy with a similar shape distribution to Wyoming Bentonite, although smaller in size.
The electron microscopic technique used is based on a positively charged supporting film which, immersed in a clay suspension, preferentially selects negatively charged montmorillonite from the predominantly uncharged impurities. A conventional replica technique also showed lath-shaped particles in the blue clay.
The possible practical consequences of the different particle shapes are discussed.