Final answer:
Igneous rocks are classified by their composition and texture. Composition is determined by the minerals present due to the original molten material, while texture is a result of the cooling history. Different tectonic environments produce specific types of igneous rocks.
Step-by-step explanation:
Composition and Formation of Igneous Rocks
Igneous rocks are classified into different types based on two main factors: composition and texture. The composition of an igneous rock refers to the minerals that are present within it, which can vary based on the original molten material. For example, rocks with high silica content, such as granite, are rich in quartz and feldspar, while those with low silica content, like basalt, have more pyroxene and olivine.
The texture of an igneous rock reveals the history of its cooling process. Intrusive igneous rocks, such as granite, cooled slowly beneath the Earth's surface, resulting in a coarse-grained texture. Conversely, extrusive igneous rocks, like basalt, cooled quickly on the Earth's surface, leading to a fine-grained or glassy texture.
Different tectonic environments are associated with the formation of specific igneous rocks. Mid-ocean ridges, for example, are typically associated with basaltic rocks due to the rapid cooling of magma. Subduction zones often give rise to granitic compositions as a result of the melting of continental crust material influenced by the addition of water from the subducting oceanic plate.