Here's why:

* Elements are pure substances made up of only one type of atom (like oxygen, gold, or carbon).

* Compounds are made up of two or more different elements chemically combined (like water, which is made of hydrogen and oxygen).

Pumice is a volcanic rock formed when lava with a lot of trapped gas cools rapidly. It's mainly made up of silica (silicon dioxide), but also contains other elements like aluminum, iron, magnesium, and calcium.

So, pumice is a mixture of different minerals (which are themselves compounds), making it a rock, not an element or compound.