* Grain Size: Gabbro has large, visible crystals (called phaneritic texture). This indicates that the magma cooled slowly underground, allowing ample time for crystals to grow.

* Mineral Composition: Gabbro is typically composed of plagioclase feldspar and pyroxene. These minerals are common in mafic (dark-colored) igneous rocks.

* Cooling Environment: Intrusive rocks form when magma cools and crystallizes beneath the Earth's surface. Extrusive rocks form from lava that cools and solidifies on the surface. Gabbro's mineral composition and large crystals are consistent with a slow cooling process that occurs underground.

In contrast, extrusive rocks like basalt have fine-grained textures due to their rapid cooling on the surface.