Igneous Igneous RocksRocks

The Nature of Igneous The Nature of Igneous RocksRocks

All igneous rocks are made of interlocking All igneous rocks are made of interlocking crystals of minerals that cool and crystallize crystals of minerals that cool and crystallize our of magma.our of magma.

Minerals are compounds of chemical elements.Minerals are compounds of chemical elements.

There are 6 types of minerals that are common There are 6 types of minerals that are common in igneous rocks. They are: quartz, micas, in igneous rocks. They are: quartz, micas, feldspars, pyroxenes, amphiboles, and olivines.feldspars, pyroxenes, amphiboles, and olivines.

MagmaMagma – It is a natural occurring molten rock – It is a natural occurring molten rock material, generated within the Earth, from material, generated within the Earth, from which igneous rocks are formed from.which igneous rocks are formed from.

Magma, Lava, and Magma, Lava, and Igneous RockIgneous Rock

Every kilometer into the earth you go, the Every kilometer into the earth you go, the temperature goes up about 30 degrees temperature goes up about 30 degrees Celsius. Celsius.

At about 100 km to 350 km into the Earth, At about 100 km to 350 km into the Earth, the temperature is great enough to melt the temperature is great enough to melt rock, and this melted rock is magma.rock, and this melted rock is magma.

Magma is less dense than the rock around it, Magma is less dense than the rock around it, so it rises, like a hot air balloon. so it rises, like a hot air balloon.

Remember hot is less dense than cold, that Remember hot is less dense than cold, that is why hot air rises.is why hot air rises.

Intrusive Igneous RockIntrusive Igneous Rock

This type of rock forms underneath the This type of rock forms underneath the surface of the Earth. surface of the Earth.

It is called “Intrusive” because the magma It is called “Intrusive” because the magma intrudes into rock that is already there.intrudes into rock that is already there.

Extrusive Igneous RockExtrusive Igneous Rock

When magma cools on the surface, it is When magma cools on the surface, it is called extrusive igneous rock, because the called extrusive igneous rock, because the magma (now called lava since it is on the magma (now called lava since it is on the surface) “extruded” onto the Earth’s surface) “extruded” onto the Earth’s surface like toothpaste from a tube.surface like toothpaste from a tube.

How to classify How to classify Igneous RocksIgneous Rocks

There are two ways to classify igneous rocks:There are two ways to classify igneous rocks: ColorColor TextureTexture

ColorColor

The minerals inside an igneous rock determine the The minerals inside an igneous rock determine the color. color.

Light color minerals are: quartz, feldspar, and mica.Light color minerals are: quartz, feldspar, and mica.

Dark color minerals tend to be pyroxenes, Dark color minerals tend to be pyroxenes, amphiboles, feldspar, mica, and olivines.amphiboles, feldspar, mica, and olivines.

How to classify How to classify Igneous RocksIgneous Rocks

TextureTexture The crystal size of an igneous rock depends The crystal size of an igneous rock depends

on how fast or slow the magma cools.on how fast or slow the magma cools. Slow cooling magma means large crystalsSlow cooling magma means large crystals Fast cooling magma means many small Fast cooling magma means many small

crystalscrystals If lava cools really fast, it may result in a If lava cools really fast, it may result in a

glassy looking rock.glassy looking rock.

Lithospheric Plates and Lithospheric Plates and Igneous RocksIgneous Rocks

Lithospheric PlatesLithospheric Plates – a rigid, thin segment of the – a rigid, thin segment of the outermost layer of the Earth, consisting of the Earth’s outermost layer of the Earth, consisting of the Earth’s crust and part of the upper mantle. The plate can be crust and part of the upper mantle. The plate can be assumed to move.assumed to move.

Convergent BoundaryConvergent Boundary – A boundary line where – A boundary line where lithospheric plates are moving towards each other.lithospheric plates are moving towards each other.

Divergent BoundaryDivergent Boundary – A boundary line that is getting – A boundary line that is getting wider as lithospheric plates move away from each other.wider as lithospheric plates move away from each other.

Transform BoundaryTransform Boundary – A boundary line where two – A boundary line where two lithospheric plates are sliding past each other. Like two lithospheric plates are sliding past each other. Like two cars on a road.cars on a road.