Here's why:

* Granite is a felsic igneous rock, meaning it's rich in silica and light-colored minerals like quartz and feldspar.

* When granite melts, it forms a felsic magma. This magma is very viscous (thick) due to its high silica content.

* As the magma rises and erupts on the Earth's surface, it cools quickly. This rapid cooling doesn't allow large crystals to form, resulting in a fine-grained, often glassy texture.

* Rhyolite is the extrusive equivalent of granite, meaning they share the same chemical composition but have different textures due to their cooling conditions.

Let me know if you'd like to know more about igneous rocks!