Chapter 5 – Igneous Rocks

What are Igneous Rocks? Igneous rocks are formed from the crystallization of magma Lava is the rock that flows out of the Earth’s surface

Types of Igneous Rocks Fine-grained rocks that cool quickly on Earth’s surface are called extrusive rocks Coarse-grained igneous rocks that cool slowly beneath Earth’s surface are called intrusive rocks Granite is the most common intrusive igneous rocks

Composition of Magma Magma is often a slushy mix of molten rock, gases, and mineral crystals The elements found in magma are the major elements found in Earth’s crust: oxygen, silicon, iron, aluminum, magnesium, calcium, potassium, and sodium Silica (SiO2) is the most abundant and has the greatest effect on magma characteristics There are 3 types of magma – basaltic, rhyolitic, andesitic

Origins of Magma In lab, most rocks must be heated to temps around 800-1200 degrees Celsius before they melt In nature these temps are found in the upper mantle and lower crust

Partial Melting Not all minerals have the same melting points – because of this not all parts of the rock melt at the same time This explains why magma is often a slushy mix of crystals and molten rock Partial melting is when some minerals melt at low temps and other minerals remain solid