GEOLOGICAL ASPECTS OF CALCITE MICROSTRUCTURE

High voltage transmission electron microscopy is used to reveal and interpret the microstructures of a variety of calcitic rocks of differing origins and histories. The survey includes undeformed fine-grained limestones and suites of marbles with a wide range of metamorphic grade, shock-deformed limestones from meteorite impact craters and a few carbonatites. It is shown that the microstructures generally conform with metamorphic grade, but that heterogeneities in the microstructure complicate the interpretation. These heterogeneities are attributed to late deformational and thermal events which cause over-printing. Ease of overprinting in calcite is attributed to the relatively low flow stresses and ease of recovery for calcite vis-à vis other rock-forming minerals. © 1979.