Residual cipolino: end-product of calcareous rocks in regional metamorphism.

Intercalations of banded rocks of quartzitic appearance, consisting of an equigranular mosaic of quartz and basic plagioclase with interspersed large crystals of diopside, hornblende, and garnet, are fairly common in high-grade metamorphic terranes. These rocks, variously named plagioclase-granulites, diopside-granulites, calc-silicate granulites, feldspathic pyroxenites, silicated carbonate rocks, etc., are derived from normal limestones and dolomites with average contents of impurities, from which CaCO3, MgCO3, and, possibly, minor potassium have been leached in the course of metamorphism. Small amounts of Ca and Mg, reacting with the impurities, gave rise to Ca-Mg-silicates. As these rocks have developed from marbles, with an intermediate stage of CaMg- silicate bearing marbles (cipolinos), into calcite-free Ca-Mg-silicate rocks, the name 'residual cipolino' is proposed for such rocks.