The “Action of hydrogen peroxide on weathered mica” was described very recently by Drosdoff and Miles. These investigators noticed that treatment of soil samples with H2O2 to destroy organic matter caused the exfoliation of decomposed mica. They ascribed this reaction to the presence of traces of catalytic MnO2 chiefly, which caused the decomposition of H2O2. The liberated oxygen forced the sheets of the mineral apart. They also found that the addition of a few drops of ammonium hydroxide accelerated the reaction considerably. The writer repeated these experiments and extended them to analyzed vermiculites with the idea of introducing between the layers ions which would restore the structure to the original one, which was that of biotite in most cases.