Knowra Igneous rock Igneous rock Igneous rock forms when molten magma or lava cools and solidifies. Its mineral grains and textures record how quickly it cooled and where solidification occurred.
Magma : Molten or partially molten rock beneath Earth’s surface, containing dissolved gases and solid crystals. Magma becomes intrusive igneous rock when it cools underground.
Silicate minerals : Minerals built chiefly from silicon and oxygen, commonly with other elements. Most igneous rocks are dominated by minerals in this broad family.
Granite : A coarse-grained felsic intrusive igneous rock composed mainly of quartz and feldspar. Granite exemplifies slow crystallization of silica-rich magma underground.
Sedimentary rock : Rock formed through the accumulation, compaction, or chemical precipitation of sediment. Unlike igneous rock, it forms from sediment rather than solidifying melt.
Volcanic arc : A chain of volcanoes formed above a subduction zone. Arc lavas reveal how water released from a descending slab promotes magma formation.
Lava : Molten rock that has reached Earth’s surface. Lava solidifies into extrusive igneous rock after eruption.
Felsic : A compositional category for igneous rocks and magmas rich in silica and feldspar-forming elements. Felsic composition distinguishes granite and rhyolite from darker, iron-rich rocks.
Rhyolite : A fine-grained felsic volcanic rock, commonly compositionally similar to granite. Rhyolite illustrates how rapid surface cooling preserves a felsic composition in fine grains.
Metamorphic rock : Rock transformed from preexisting rock by heat, pressure, or chemically active fluids without melting completely. Metamorphism alters solid rock, whereas igneous formation involves molten material.
Mid-ocean ridge : A long underwater mountain chain where tectonic plates separate and new oceanic crust forms. Basaltic rocks at ridges record the creation of oceanic crust.
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