card
243

granite

OLogy Series
geology
card
243

granite

OLogy Series
geology

Granite is an igneous rock, which means it formed from magma, or melted rock. It forms deep inside the Earth under a mountain or volcano when melted rock cools or crystallizes into solid rock. Over time, wind, ice, and water wear away at the mountain or volcano above it, and the granite is exposed to the surface. Granite is used as a building material because it's a hard stone.

Granite forms in pockets of magma miles below the Earth's surface called:

magma holes

magma chambers

volcanoes

Are you right?

Correct!

Magma chambers are holding spaces for magma, which is found within the crust, often under mountains and volcanoes. When the magma cools, granite is formed.

Granite can have very large crystals. That's because when it formed, the magma:

cooled slowly

cooled quickly

never cooled

Are you right?

Correct!

Granite has large grains because the magma cooled slowly. This allows crystals to grow very big.

Christine Tappen, Earth scientist

Granite forms when igneous rock cools deep within the Earth. The slower it cools, the larger its mineral size. Pegmatitic granite has minerals as big as 10 meters (33 feet) wide!

Granite is always gray.

Fact
or
Fiction
?

Fiction

Granite is often speckled with dark and light colored minerals, and comes in a variety of colors like gray, pink, blue, green, and purple.

The Earth's continental crust is made of granite.

Fact
or
Fiction
?

Fact

Granite makes up most of the continental crust, while another igneous rock called basalt makes up the oceanic crust.

Definition: a rock that forms when magma cools deep in the Earth's crust
Type: igneous
Appearance: typically light and dark speckles, with large crystals
Primary minerals: feldspar, quartz, and mica
Cool fact: Built in the second century B.C. and still standing today, the Great Wall of China is made of granite and other rocks.

Image credits: courtesy of AMNH; Christine Tappen: courtesy of AMNH.