Final answer:
Igneous rocks are classified based on their composition and texture, which are determined by the original molten material's make-up and the rock's cooling process. These factors affect properties like mineralogy and grain size, as well as the rock's overall color.
Step-by-step explanation:
The classification of igneous rocks is primarily based on two major properties: the original composition of the molten material (magma or lava) and the cooling process that the material underwent to form the rock.
Specifically, these properties are the composition and texture of the igneous rock, which include factors such as the chemical make-up or the types of minerals present, as well as the size of the mineral grains or the presence of structures such as vesicles or glass shards within the rock.
Igneous rocks with large mineral grains, forming as magma cools slowly inside the Earth, are known as intrusive or plutonic rocks. Conversely, rocks with tiny grains that cool quickly on the Earth's surface are referred to as extrusive or volcanic.
Moreover, the color of the igneous rock, influenced by the minerals' chemistry, can provide diagnostic clues for classification, with darker colors indicating the presence of iron and magnesium-bearing minerals and lighter colors suggesting the presence of minerals rich in potassium, aluminum, and silica.