Download Igneous Rocks

What are the two types of
igneous rocks?
Igneous Rocks
Born of Fire!
Igneous Rocks
Igneous = fire-formed; products of
cooling and crystallization of magma
Magma = molten rock beneath surface
Lava = molten material on surface
What is magma?
Three components:
– Liquid = melted rock
– Solids = crystals
– Volatiles = dissolved gases
 Water (H2O)
 Carbon dioxide (CO2)
 Sulfur dioxide (SO2)
Igneous Rocks
Classified by:
 Texture (presence/absence of crystals)
 Intrusive (formed under surface)
 Extrusive (formed on surface)
 Composition (elements present)
 Mafic
 Intermediate
 Felsic
Rock Composition
& source

Felsic: light color, aluminum and silicon
rich ~ from thick lava
– These are formed from continental material

Mafic: dark color, more calcium and iron
with little silicon ~ thinner lava
– These are formed from oceanic crust
Texture and grain size
Texture indicates the rate of cooling of the
magma.
Coarse grained (intrusive) igneous rocks cool
relatively slowly inside the Earth.
Fine grained (extrusive) igneous rocks (rhyolite
& basalt) cool relatively quickly as lava at or near
the Earth’s surface.
Some extrusive igneous rocks cool so quickly
that their texture is glassy (obsidian).
Color and composition
• The color (light, dark, or intermediate)
indicates the origin and composition of the
magma.
• Light colored igneous rocks come from
relatively near the Earth’s surface and consist
of low density minerals; quartz, potassium
feldspar, muscovite mica.
• Dark colored igneous rocks come from the
upper mantle (asthenosphere) and consist of
higher density minerals such as calcium rich
plagioclase feldspar.
Igneous rock formed from magma
or lava
The two types are:
 1. Intrusive
 2. Extrusive

Igneous Rock Textures

Extrusive Rocks
– Cool quickly at the
surface
– Have small crystals
(fine-grained)

Intrusive Rocks
– Cool slowly below
the surface
– Have large, visible
crystals
(coarse-grained)
Intrusive igneous rocks
Magma cools slowly underground
 These are also called plutonic
 The slow cooling allows larger crystals to
grow
 Large crystals make a coarse-grained rock
 Granite is a good example

Intrusive granite
Gabbro - Intrusive
Extrusive Igneous rocks
Lava cools quickly above ground
 Also called volcanic
 Quick cooling creates small or no crystals
 Smaller crystals make a fine-grained rock.
 Basalt is a good example

Obsidian - Extrusive
Scoria - Extrusive
Pumice- extrusive
Andesite - Extrusive
Rhyolite - Extrusive
Basalt
Which type of sedimentary rock
is this?