Final answer:
The texture of an igneous rock is determined by the cooling rate of the magma or lava and the original composition of the molten material, resulting in different grain sizes and classifications.
Step-by-step explanation:
The texture of an igneous rock depends primarily on the original composition of the molten material and the cooling process. When magma cools slowly inside the Earth, large crystals form, resulting in a coarse-grained texture known as plutonic or intrusive. Conversely, when lava cools quickly on the Earth's surface, the crystals are small, leading to a fine-grained texture known as extrusive or volcanic. The size of the mineral grains reflects the cooling rate, and the composition of the minerals determines the rock's color and overall classification.