Retention of Carbon Dioxide Bubbles on Calcite Etch-Peaks

Abstract

THE etch-patterns on cleavage faces of calcite which have been reported1–3 bear some interesting similarities and dissimilarities to etch-patterns obtained in this Laboratory. Watts etched calcite for 30 sec. in 1 per cent nitric acid and obtained five-sided figures which he called pits. We immersed calcite in 0.001 N hydrochloric acid for one week and obtained essentially six-sided peaks (Fig. 1) with irregular valleys between them. The sixth side has a rougher surface than the other sides and it seldom extends to the apex of the peak. It may constitute an incompletely formed figure. Stanley used 10 per cent hydrochloric acid for 10–60 sec. and obtained figures which he describes as four-sided, although from his published photographs we detect a tendency of these figures toward the six-sided etch-patterns observed in our study. The Pandyas, using ammonium chloride, obtained parallelograms.