Chapter 4, section 2 – Igneous Rocks
Classifying Igneous rocks
1. Classified according to their origin
texture, and mineral composition.
2. Extrusive rock is formed from lava that
erupted onto the Earth’s surface. Basalt
is the most common extrusive rock.
3. Intrusive rock is formed when magma
hardens beneath the Earth’s surface.
Granite is the most common intrusive
rock.
Texture
1. Rapidly cooling lava form fine-grained
rocks with small crystals. Slowcooling magma form coarse-grained rocks
with large crystals.
2. Intrusive rocks usually have large
crystals. Extrusive rocks usually have
small crystals.
Mineral composition
1. Most of the Earth’s minerals contain
silica.
2. High silica content, the rocks are lightcolored. Low silica content, rocks are
dark colored.
Uses of Igneous rocks
1. Throughout history have been used for
tools and building materials.
2. Granite is an example of a building
material used in the construction of
bridges and buildings.
3. Pumice is used for cleaning and
polishing. Obsidian was used to make
sharp tools.