Here's why:

* Mafic: Basalt is a mafic igneous rock, meaning it is rich in magnesium and iron, giving it a dark color.

* Holes: The holes are called vesicles. They form when gases trapped within the molten rock escape as it cools and solidifies.

* Dense Materials: Despite the holes, the rock is still considered dense because it's primarily made of heavy minerals like pyroxene and plagioclase feldspar.

Note: While the holes make the rock appear less dense, the overall material density remains high due to the heavy minerals present.

Let me know if you have any other questions!