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

Igneous Rock Igneous (ig-nee-us) rock forms when molten rock cools and solidifies. (on the surface) (under the surface) - 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 Basaltic igneous rocks are dense, heavy rocks most often made of dark colored minerals. The are often rich in iron and magnesium. Basalt – a dark colored, fine grained, extrusive rock Scoria – forms when magma cools with gas bubbles inside

Igneous Rocks Granitic igneous rocks are made of less dense and lighter colored minerals. Pumice – cools from gas filled molten rock. Pumice can float in water since its density is so low. Granite – showing the light colored mineral grains. Granite is a well known rock, and comes in many forms.

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.

Igneous Rocks Igneous rocks can also be basaltic or granitic. Basaltic rocks are made of higher density, darker-colored minerals Granitic rocks are made of lower density, lighter- colored minerals.