Download Igneous Rocks - Social Circle City Schools

Igneous Rocks
Chapter 2 Sec. 3 pg. 58
I. Classifying Igneous rocks- igneous rocks are any rocks
formed by magma or lava
Ignis means fire
“fire rocks”
Igneous rocks are classified by their origin, texture, and
mineral composition
1. Origin- describes where the rock is formed
A. Extrusive rocks- formed above ground, rocks formed
by lava that has erupted, basalt is the most abundant
extrusive rock
B. Intrusive rocks- formed under ground by hardened
magma, granite is the most abundant intrusive rock
2. Texture-the texture depends on the size and shape of the
mineral crystals.
Rapidly cooling lava forms find grained rocks with small
crystals, so extrusive rocks have a fine grained or glassy
texture
Slowly cooling magma form coarse grained rocks with
large crystals, so intrusive rocks have larger crystals then
extrusive rocks
Some extrusive rocks harden so rapidly that they have no
crystal structure and look shiny like glass, obsidian is an
example.
3. Mineral composition- Most of Earth’s minerals contain
silica
Silica- is a material formed from oxygen and silicon.
Lava and magma that are high in silica usually form
lighter colored rocks
Lava and magma with low silica form darker rocks
The colors of the minerals particles in a rock affect the
color of the rock.
II. Uses of Igneous Rocks- people throughout history have
used igneous rocks for tools and building materials.
1. Building Materials- some examples of igneous rocks
used as building material are
Granite- used for statues, bridges, and paving streets
Basalt- ground up to make gravel
2. Other UsesPumice-used for polishing and cleaning
Obsidian-used for making sharp tools