* Cooling Rate and Grain Size: The rate at which magma or lava cools determines the size of the crystals that form in the igneous rock. Slow cooling allows for larger crystals to grow.

* Granite: Granite is an intrusive igneous rock, meaning it cools slowly underground. This slow cooling allows for the formation of large, visible crystals, giving granite its characteristic coarse-grained texture.

* Pumice: Pumice is an extrusive igneous rock, meaning it cools quickly on the Earth's surface. This rapid cooling results in tiny, microscopic crystals, giving pumice its frothy, porous texture.

In summary:

* Intrusive rocks (like granite) cool slowly, forming large crystals.

* Extrusive rocks (like pumice) cool quickly, forming small crystals.