Igneous Rocks
Chapter 2 Sec. 3
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
Origin- describes where the rock is formed
Extrusive rocks- formed above ground, rocks formed by lava that
has erupted, basalt is the most abundant extrusive rock
Intrusive rocks- formed under ground by hardened magma, granite
is the most abundant intrusive rock
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 intrusive rocks
Some extrusive rocks harden so rapidly that they have no crystal
structure and look shiny like glass, obsidian is an example.
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.
Uses of Igneous Rocks- people throughout history have used
igneous rocks for tools and building materials.
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
Other UsesPumice-used for polishing and cleaning
Obsidian-used for making sharp tools