calcium carbonate

/K AE1 L S IY0 AH0 M K AA1 R B AH0 N EY0 T/
noun
  1. 1

    A colourless or white inorganic compound, CaCO3, occurring as chalk, limestone, marble etc; reacts with acids to liberate carbon dioxide.

Source: https://en.wiktionary.org/wiki/calcium%20carbonate