Abstract
Pyrite crystals were examined with the aid of a phase-contrast microscope. Dark lines and small spots, both corresponding to depressions less than 20Å in depth, were observed along edges of growth layers on the surfaces, and these are considered to have been formed by preferential etching, respectively along the steps of growth layers and at such imperfections as vacancies or impurity sites. These etch features have close similarity with those reported by the Sunagawa on hematite, and are considered to be two-dimensional ones characteristic of the earliest stage of weak etching.
