Final answer:
Igneous rocks are classified by texture and mineral composition, derived from magma's cooling rate and chemistry. Intrusive rocks like granite have large grains and form under slow cooling conditions, while extrusive rocks like rhyolite have fine grains and cool rapidly. Tectonic settings such as divergent plate boundaries often produce basaltic rocks.
Step-by-step explanation:
Igneous rocks are categorized based on their texture and mineral composition, reflecting their formation processes. The original composition of the molten material and the cooling rate of this material are crucial in defining these characteristics. Mineral composition is dependent on the chemistry and temperature of the magma, which determines the minerals that crystallize from it. Rocks with large grains are called intrusive or plutonic, suggesting slow cooling within the Earth. Conversely, rocks with fine grains are known as extrusive or volcanic, indicating rapid cooling on the Earth's surface.
Examples of common igneous rocks include granite, composed mainly of feldspar and quartz, with minor hornblende and biotite, indicating a coarse-grained, intrusive texture. An extrusive counterpart, with small mineral grains, would be rhyolite, having a similar composition. Tectonic environments influence formation; for instance, divergent plate boundaries and hotspots typically produce basaltic magmas, leading to the formation of basalt when extrusive and gabbro when intrusive.