Abstract
Cleaved surfaces in biotite mica have been investigated using high-resolution TEM with the beam direction parallel to the cleaved surfaces to reveal the location of some potassium ions. Numerous (001) cleavages were formed along thin edges of the crystals, probably due to tensile strain induced by ion milling sample preparation. The cleavages are formed at interlayer positions in the biotite structure and opposing cleavage surfaces have distinct contrasts in atomic-resolution electron micrograph. In part, the contrast difference is explained by multislice image simulation calculated for the model where a certain amount (about half a monolayer in the maximum) of potassium ions are located on one side of the cleavage and few potassium ions are located on the other side. Some cleavages are healed by beam radiation, leaving no trace in the structure image of the recovered interlayer, indicating diffusion of potassium into the interlayer from the specimen surfaces.
