Here's the breakdown:
* Calcium carbonate (CaCO3) is a chemical compound formed by the elements calcium (Ca), carbon (C), and oxygen (O).
* Marble is a metamorphic rock formed when limestone (which is also primarily composed of calcium carbonate) is subjected to heat and pressure.
So, while marble is mainly made up of calcium carbonate, it's not a compound itself. It's a rock containing the compound calcium carbonate as its primary constituent.