Liquid magma is less dense than the solid rock it comes from.

Here's why:

* Thermal expansion: When rock melts into magma, the atoms and molecules gain energy and spread out, leading to an increase in volume.

* Density = Mass / Volume: Since the volume increases while the mass remains the same, the density decreases.

This lower density is the reason why magma rises through the Earth's crust and eventually erupts at the surface.