Here's why:

* Composition: Granite is made up of minerals like quartz, feldspar, and mica. These minerals are relatively dense. The mantle, on the other hand, is primarily composed of denser minerals like olivine and pyroxene.

* Density: The average density of granite is around 2.65 g/cm³, while the mantle rocks have densities ranging from 3.3 to 5.5 g/cm³.

So, granite is NOT less dense than rocks in the Earth's mantle. It's actually less dense than the Earth's crust but denser than the mantle.

Here's why granite is found in the Earth's crust:

* Formation: Granite forms from the slow cooling and crystallization of magma (molten rock) deep within the Earth's crust.

* Buoyancy: While granite is denser than the surrounding crustal rocks, it's less dense than the mantle. This density difference allows granite to rise through the crust and eventually solidify at the surface.

Therefore, granite's location in the Earth's crust is due to its relative density compared to the surrounding rocks, not the mantle.