Here's why:

* Metamorphism: Marble is formed when limestone undergoes metamorphism. This means the limestone is subjected to intense heat and pressure, causing it to recrystallize and transform into marble.

* Mineral Composition: Both limestone and marble are primarily composed of calcium carbonate (CaCO3). However, the recrystallization process in marble results in a denser, more tightly packed structure with larger crystals.

Let me know if you have any other rock-related questions!