Abstract
X-ray and chemical data of some specimens of pyrophyllite from Japan were discussed. The k=3n reflections are predominant; this fact suggests that layers randomly displaced by multiples of 1/3b0 are dominant.
X-ray studies on ignited specimens have made clear a thermal transformation at 700°C, which agrees with the concept proposed by Bradley and Grim.
X-ray, thermal and chemical data on the 25Å-clay mineral found in association with a certain specimen of pyrophyllite were discussed. The clay mineral agrees with a regularly interstratified pyrophyllite-montmorillonite.
