Igneous Rocks

Anticipation guide #3 1) Igneous rocks were the first rocks created on Earth 2) Basalt is a rock that makes up the continents 3) Rocks can be classified by mineralogy, texture and process 4) The size of the crystals in rocks depends on the solidification rate 5) Granite is an extrusive rock

VA SOL SOL 5 The student will investigate and understand common rock types based on mineral composition and textures and the rock cycle as it relates to the origin and transformation of rock types. Key concepts include a. igneous (intrusive and extrusive) rocks;

Objective Classify igneous rocks by mineral content and texture. Intrusive – granite; Extrusive – pumice, obsidian, and basalt.

Enduring Understanding The rock cycle is an ongoing process by which rocks are formed. It gives us an explanation of how Earth materials are recycled through time. Virginia has many natural resources.

Igneous Rocks Minerals combine in the Earth’s crust to form rocks. Most rocks are made of one or more minerals. Igneous rocks were the first type to form on Earth as its molten surface cooled and solidified

Igneous Rocks Igneous Rocks form from the crystallization of magma

Igneous Rocks Magma is molten rock below Earth’s surface

Igneous Rocks Lava is magma that flows out onto Earth’s surface

Igneous Rock Types Igneous rocks are classified based upon where they form Extrusive igneous rocks cool quickly on the surface and are fine-grained (small crystals)

Igneous Rock Types Rhyolite is the most common extrusive igneous rock

Igneous Rock Types Other common extrusive igneous rocks include pumice, obsidian, and basalt Pumice Obsidian Basalt

Igneous Rock Types Intrusive igneous rocks cool slowly beneath the surface and are coarse-grained (larger crystals)

Igneous Rock Types Granite is the most common intrusive igneous rock

Magma Magma is often a slushy mix of molten rock, gases and mineral crystals. The elements in magma are the same major elements found in the Earth’s crust: oxygen (O), silicon (Si), aluminum (Al), iron (Fe), magnesium (Mg), calcium (Ca), potassium (K), and sodium (Na)

Magma Silica (SiO2) is the most common compound in magma and has the greatest effect on its characteristics Rhyolitic magma has an SiO2 content of 70% Andesitic magma has an SiO2 content of 60% Basaltic magma has an SiO2 content of 50%

Magma Formation There are four main factors that affect magma formation Temperature. Heat comes from the remaining energy from Earth’s formation and the decay of radioactive elements

Magma Formation Pressure. The pressure increases with depth

Magma Formation Water content. More decreases the melting point of the rocks

Magma Formation Mineral content. Minerals melt at different temperatures

Classifying Igneous Rocks Extrusive and intrusive igneous rocks are further classified by their mineral compositions

Classifying Igneous Rocks Felsic rocks are light colored, have high silica contents, and contain quartz and the feldspars orthoclase and plagioclase Granite is the most common felsic rock

Classifying Igneous Rocks Intermediate rocks are darker than felsic and have moderate amounts of biotite, amphibole, and pyroxene Diorite is a good example of an intermediate rock

Classifying Igneous Rocks Mafic rocks are dark, have lower silica contents and are rich in iron and magnesium Basalt is a mafic rock

Classifying Igneous Rocks Ultramafic rocks have low silica contents and very high levels of iron and magnesium. Olivine is an ultramafic rock

Bowen’s Reaction Series As magma cools, minerals form in predictable patterns. The reaction series has two main branches of crystallization

Bowens Reaction Series

Bowen’s Reaction Series Feldspars undergo a continuous change in composition. The first to form are rich in calcium and as cooling continues the feldspars react with the magma and change to sodium rich Iron-rich minerals undergo abrupt changes during fractional crystallization

Bowens Reaction Series

Bowen’s Reaction Series As minerals form in the order shown in Bowens reaction series, elements are removed from the remaining magma. Silica and Oxygen are the most abundant elements and are left over at the end of the reaction series. The remaining magma finally crystallizes to form quartz.

Bowens Reaction Series