What are Igneous Rocks? Chapter 5.1. Formation of Igneous Rock Magma – molten rock beneath the Earth’s surface. Lava – magma that flows out onto the Earth’s.

What are Igneous Rocks?

Chapter 5.1

Formation of Igneous RockMagma – molten rock beneath the Earth’s surface.Lava – magma that flows out onto the Earth’s surface.

Igneous rock forms when lava or magma cools and the minerals within it crystallizes.

Magma consists mainly of the elements – oxygen silicon aluminumiron magnesium calciumpotassium sodium

Magma is classified by the amount of silica (SiO4) it contains.- Silica content affects melting temperature and the thickness (viscosity) of the magma.

Bonus Questions!1. What is the difference between magma

and lava?

2. What determines the melting point and thickness of magma?

Magma Formation- Magma is formed when rock is melted within the

Earth.- Factors affecting the formation of magma are:

1. Temperature2. Pressure 3. Water content4. Type of minerals present

Bonus Question!3. Name two factors affecting the

formation of magma?

Classification of Igneous Rocks

Chapter 5.2

Intrusive Igneous Rocks- form when magma cools slowly within the Earth’s crust.- form rocks with large crystals (coarse-grained). (magma cools slow enough for crystals to grow large)

Granite

Extrusive Igneous Rocks- form when lava cools quickly on the Earth’s surface.- form rocks with small crystals (fine-grained).(lava cools too quickly for large crystals to form)

Obsidian

Pumice

Basalt

Bonus Questions!4. Give an example of an intrusive igneous

rock.

5. Give an example of an extrusive igneous rock.

6. Which type of igneous rock has smaller crystals?

Igneous Rocks as ResourcesVeins – as the last of the molten minerals (usually

quartz) begin to crystallize, they are often squeezed into cracks in the rock to form veins.- some of the veins contain metallic elements (gold, silver, copper) that can be mined for a profit.

Pegmatites – veins of extremely large-grained crystals.

Pegmatite with blue corundum crystals (Wikipedia)

Bonus Question!7. What mineral deposit is gold usually

associated with?

Igneous Rocks as ResourcesKimberlites – vertical intrusions of hardened magma

(like the neck of a volcano).- well known for the diamonds they often contain.

Construction Resources – since igneous rocks are strong and weather-resistant making them a great building material.

Hewn kimberlite core sample from the James Bay Lowlands region of Northern Ontario, Canada. Green olivine grains and purplish red garnet are visible. The sample is 13 cm (5 inches) long. (Wikipedia)