Igneous Rock

By Mr. Krall

What is a Rock?

A rock is a mixture of minerals.

Rocks form and reform through the rock cycle.

Lava/Magma

THE ROCK CYCLE

Igneous Rock

Igneous (ig-nee-us) rock forms when molten rock cools and solidifies.

lava

magma

(on the surface)

(under the surface) molten

- means currently a liquid because it’s hot!

Igneous Rock

Anytime any other type of rock melts, and then cools back down, it becomes igneous rock.

While molten, the liquid minerals and rock will separate and sort themselves by their density.

Igneous Rock

The more dense minerals/rocks sink, and the less dense float.

When they cool back down they become a sorted stack of solid minerals and rocks. The rocks are igneous rocks.

Igneous Rock

Igneous rock is classified into two groups based on where it forms.

Igneous Rock

Extrusive Igneous Rock – forms when lava cools on the Earth’s crust.

It “exited” the crust.

Igneous Rock

Extrusive Igneous Rock has very small mineral grains since it cooled so quickly.

Obsidian – cooled so quickly you can’t even see the mineral grains.

Rhyolite – has very fine, sand-like mineral grains.

Igneous Rock

Intrusive Igneous Rock – forms when magma cools inside the Earth.

It is still “in” the Earth.

Igneous Rock

Intrusive Igneous Rock has large mineral grains since it cooled slowly.

Diorite– the dark spots are large mineral grains from slow cooling.

Granite – has a variety of colors from the mix of minerals.

Igneous Rocks

Igneous rocks are formed when molten rock cools and solidifies. Igneous rocks are the most abundant type of rocks on Earth.

Igneous rocks can be extrusive (on top of the crust) or intrusive (inside the earth.)

Extrusive rocks have fine grains because the rock cooled quickly, while intrusive rocks have large mineral grains from cooling slowly.