Igneous Rocks

• Basalt • Granite

How Igneous rocks are Formed

• Igneous rocks are called fire rocks and are formed either underground or above ground. Underground, they are formed when the melted rock, called magma, deep within the earth becomes trapped in small pockets. As these pockets of magma cool slowly underground, the magma becomes igneous rocks.

• Intrusive Igneous Rock -Granite

How Igneous Rocks are Formed

• Igneous rocks are also formed when volcanoes erupt, causing the magma to rise above the earth's surface. When magma appears above the earth, it is called lava. Igneous rocks are formed as the lava cools above ground.

• Extrusive Igneous Rocks-Basalt

Fact about Igneous Rocks

• Rock Facts • Igneous rocks are the oldest kind of rock. • Igneous rocks are formed deep inside the earth

where the temperature is very high. • The minerals in the earth are in liquid form and

are called magma. • Magma is squeezed around inside the earth and

as it pushes towards the surface of the earth, it starts to cool. As it cools, it turns to solid igneous rock.

Fact about Igneous Rocks

• Sometimes the magma cools very slowly and forms rocks.

• Igneous rocks that cool slowly deep in the earth are called Intrusive igneous rocks and have large crystals. (Granite)

• Sometimes the magma erupts from a volcano. Magma is called lava when it reaches the earth's surface. Lava cools quickly and forms igneous rocks.

• Igneous rocks that cool quickly on the surface of the earth form rocks with small crystals called extrusive rocks. (Basalt, obsidian) 

• Sometimes extrusive igneous rocks look like glass and have no crystals or mineral particles.

Texture of Igneous Rocks

• Coarse-Grained Igneous Rocks

• Intrusive Igneous rocks commonly have large mineral crystals.

• The slow cooling of the magma allows the minerals to form well developed crystals.

• Granite is an example of a Coarse-Grain Igneous Rock

Texture of Igneous Rocks

• Fine Grain Igneous Rocks

• Extrusive Igneous Rocks

• Small mineral grains that can not be seen by the unaided eye.

• These rocks formed when magma cools rapidly as in a volcanic eruption.

• Basalt is an example of fine-grain igneous rock

Composition of Igneous Rocks

• The mineral composition of Igneous Rocks is determined by the chemical composition of the magma from which the rock is formed.

• Three basic types of Igneous Rocks

• Felsic, Mafic, and Intermediate.

Felsic Rock

• Felsic igneous rocks contain large portion of silica

• Felsic igneous rocks has light coloring because the main mineral components potassium feldspar and quartz.

• Granite is a Felsic igneous rock

Mafic Igneous Rock

• Mafic igneous are formed from magma containing lower amounts of silica than the felsic igneous rocks

• The main mineral components of the rocks are plagioclase feldspar and pyroexene minerals.

• Mafic igneous rocks are usually dark in color• Basalt is an example of a Mafic Igneous Rock.

Intermediate Igneous Rocks

• Intermediate Igneous Rocks contain less silica than a Felsic igneous rock, but more silica than a Mafic igneous rock.

• Diorite is an example of an intermediate rock.

Where Igneous Rocks are Formed