When magma cools slowly within warm rock underground, it forms a phaneritic crystal texture. Here's why:

* Slow Cooling: The slow cooling process allows ample time for mineral crystals to grow large enough to be visible to the naked eye.

* Warm Surroundings: The warm surrounding rock provides a stable environment for crystal growth, preventing rapid cooling that would result in smaller crystals.

Phaneritic textures are characterized by large, well-formed, and intergrown crystals. Common examples of igneous rocks with phaneritic textures include granite, gabbro, and diorite.