Chapter 3 – 2 Igneous Rocks!
What makes a rock IGNEOUS?
Origin, texture and mineral
composition.
ORIGIN: Where the rock is formed.
Extrusive Rock is igneous rock formed from
lava that erupted onto Earth’s surface.
Basalt is the most common extrusive
igneous rock. Forms much of Earth’s land
and ocean floor.
Intrusive Rock is igneous rock that formed when
magma hardened beneath the Earth’s surface.
Granite is the most common form of
intrusive igneous rock. Granite forms the
core of many mountain ranges.
Texture of Igneous Rock – Depends upon
the size and shape of its mineral crystals.
Rapid cooling forms fine grained, small
crystal igneous rock.
Slow cooling magma forms coarse
grained rock with large crystals.
Intrusive have larger crystals than
extrusive.
Small crystal rocks that appear to have
rocks of larger crystals inside them are said
to be PORPHYRITIC.
A change in the rate of cooling creates
Porphyritic Rock.
Mineral Composition of Igneous Rocks. Most of
Earth’s minerals contain silica (sand). Rocks
containing silica are usually light colored.
Dark colored rocks, like basalt contain a
mineral called feldspar and usually have
very little silica.
Uses of igneous Rock
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Obsidian – Cutting tools
Granite – Building materials
Basalt – Crushed for construction gravel
Pumice – Abrasives for cleaning and polishes
Perlite – (heated obsidian) Soil additives