ABSTRACT
Calc-silicate rocks, also called skarn, are composed mostly of calcium-rich silicate minerals such as diopside, anorthite, grossular-andradite garnet, and wollastonite, though they may contain some calcite, quartz, and other, non-calc-silicate minerals. Calc-silicates can form directly from calcareous sedimentary or volcanic rocks (e.g., calcareous shale, carbonate mud mixed with reworked pyroclastics), in hydrothermal veins, at igneous contacts where plutons crosscut carbonate rocks (Fig. 1.9B), and at contacts between marble and silicate rock (Fig. 1.9C). Calc-silicate rocks associated with pluton contacts can form ore deposits of economic importance. Formation of calc-silicate rocks at rock contacts commonly involves exchange of chemical components, generally with marble supplying the Ca and possibly Mg, released from carbonates during decarbonation reactions, and the silicate rock supplying silica and possibly other components. Reactions between these components in the contact zone produce the calc-silicate minerals.
