IGNEOUS ROCKS
Igneous Rocks

Form from the crystallization of magma
 From
Latin “ignis” which means fire
 Most common rocks in the Earths crust by far

Two types of Igneous Rock
Extrusive



Cools quickly on the Earth’s surface
Fine-grained
Evidence
 We
can actually watch extrusive igneous rocks from as
lava cools
Intrusive



Cools slowly beneath the surface of the Earth
Coarse-grained (large/rough)
Evidence
 Cross-cutting
relationship with other rock formations
Cross-cutting




Most igneous intrusive rocks have cross-cut
something
Magma comes up through cracks in rocks
Magma the cools leaving an igneous intrusion
Granite is the most common intrusive igneous rock
Magma

Not a pure substance
 Usually
contains
 Molten
rock
 Gases
 Mineral
crystals
 Contains
the same elements found in the Earth’s crust
 Most abundant compound is Silica (SiO4)
 Found
in almost all rocks
Melting

Not all parts of magma melt at the same time
 This
concept is called partial melting
Crystallization

Not all parts of magma crystallize (harden) at the
same time
 This
concept is called fractional crystallization
 Harder substances (diamonds) harden at the same time
and are harder to melt
 Pressure causes substances to have different melting
points
Bowen’s Reaction Series

Shows the relationship between cooling magma and
mineral formation
Mineral composition


Again silica is the primary component of magma
Felsic rocks contain high levels of silica
 Resistant
to flow
 Granite, Obsidian

Mafic rocks contain low levels of silica
 “watery
stew”
 Gabbro, Basalt
Uses



Interlocking grain textures make them very strong
They are also highly resistant to weathering
These characteristics make Igneous rocks excellent
building materials.
SEDIMENTARY ROCKS
Sedimentary Rocks


Composed of small pieces of rocks that have been
broken down and deposited
Wind, water, and other forces transport sediments
to sedimentary basins which can be more than 8 km
thick.
Clastic sediments






Boulder
Cobble
Pebble
Sand
Silt
Clay
> 256 mm
256 - 64 mm
64 - 2 mm
2 – 0.062 mm
0.062 – 0.0039 mm
< 0.0039 mm



Buried Sediments experience high pressure and
temperature
This causes lithification, which is the process of
sediments turning into rock
Sedimentary rocks can also form from cementation
 Sediments
are cemented together by mineral growth
Sedimentary Uses

Evidence of past events and life
 Due

to the presence of fossils
Energy sources
 Oil
 Natural
 Coal
gas
METAMORPHIC ROCKS
Metamorphic Rocks


From the Greek “meta” meaning change, and
“morphe” meaning form
Rock is buried and experiences great pressure and
temperature, but doesn’t quite melt
 Very

common in “mountain-building” areas
During metamorphism, rocks change form while
remaining solid
Types of metamorphic rock

Foliated
 Minerals
with flat needle-like structures line up in wavy
layers and bands

Non-foliated
 Mineral
grains lack the flattened structure
Rock Cycle

The remaking of rocks