Here's why:

* Igneous rocks are formed from the cooling and solidification of magma or lava.

* Sedimentary rocks are formed from the accumulation and cementation of sediments.

* Metamorphic rocks are formed when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are transformed by heat, pressure, or chemical reactions.

Marble is formed when limestone (a sedimentary rock) is subjected to heat and pressure, causing the calcite crystals to recrystallize and form a new, denser rock.