Why do igneous rocks have different textures?
The rate of cooling, the composition of the magma, and the location of the cooling.
The faster the magma cools that smaller the crystals that are formed.
Some magma from which the igneous rocks is form come from different combinations of remelted igneous rocks, metamorphic rocks and sedimentary layers. Some magma that is formed at divergent boundaries comes directly from the mantle. The different sources of the melted material affects the textures of the igneous rocks.
Also the amount of atmospheric gases and water that is mixed with the melted rock will affect the texture of the igneous rock. If the igneous rock is formed under the water this will have an effect on the texture. If the igneous rocks cools in the air like pumice gases will be trapped in the igneous rocks.
Granites are formed under the surface of the earth, basalts are usually formed on the surface of the earth.
So the texture of igneous rocks is affected by the rate of cooling, where the cooling takes place and the composition of the materials that make up the igneous rocks