Download Rock Notes

Types of Rocks:
1. Igneous
2. Sedimentary
3. Metamorphic
Igneous Rocks
•Rocks that forms when magma cools and hardens.
•Form by solidification (crystallization) of melted minerals.
•At the surface, LAVA hardens to form EXTRUSIVE
rocks with tiny (FINE-GRAINED) crystals or GLASSY
(no crystal) textures.
•Beneath the surface, MAGMA hardens to form
INTRUSIVE rocks with easily visible (COARSEGRAINED) crystal texture.
2 groups of Igneous Rock
•Intrusive igneous rock – The slow cooling of
magma deep below the crust.
Slow loss of heat  Long time  large, well
developed
crystal grains.
•Extrusive igneous rock – The rapid cooling of lava
on the earth’s surface.
Fast loss of heat  Short time  Can’t form
large crystals
Granite
Rhyolite
Mineral Composition
•Felsic: igneous rocks rich in light-colored
minerals such as orthoclase and quartz
•Mafic: igneous rocks rich in dark-colored
ferromagnesian minerals
Igneous Examples
•Dark-colored, fine- grained, extrusive
•Formed where lava erupted onto surface
•Most widespread igneous rock
Igneous Examples
•Natural volcanic glass
•Forms when lava cools very
quickly
•Usually dark, but small pieces
may be clear
•Fractures along curved
(conchoidal) surface
•Light
colored, frothy
(many air spaces)
Pumice
Obsidian
Sedimentary Rocks
•Formed from the compaction and
cementation of loose, solid particles
(aka sediment).
•Types of Formation:
1. Lithification of sediment
2. Precipitation from solution
3. Consolidation of organic remains
Types of Formation
CEMENTATION
COMPACTION
Lithification
Types of Formation
Precipitation
Sedimentary Rock Groups
• CLASTIC:
Comprised of
cemented sediment
• CHEMICAL:
Precipitation of
minerals from
solution
• ORGANIC:
From the remains
of organisms
Sedimentary Examples
Conglomerate
Breccia
Rounded
Angular
Sedimentary Examples
Coquina:
Type of limestone made
up of fossil shells with
little or no matrix
Fossiliferous
Limestone: Contains
the remains of ancient
plants + animals, known
as fossils
Metamorphic Rocks
• Formed when existing rocks undergo great
amounts of heat + pressure.
– Minerals recrystallize to form new minerals
– Minerals change in size + shape
– Minerals may line up in parallel bands
* All of this creates a new rock!
Controlling Factors
of Metamorphism
1. Parent Rock composition
2. Temperature: certain minerals are
unstable under specific temperatures
3. Time: the longer it takes for
metamorphism to occur, the more
change that occurs
4. Pressure: increases as depth into the
Earth’s crust increases
Types of Metamorphism
1. Contact Metamorphism:
 magma comes into contact with existing
rock
 heat from the magma can change the
structure + mineral makeup of that rock.
Types of Metamorphism
1. Regional Metamorphism:
 occurs over a large area
changes that take place at great depth
(more than 5km) below ground
related to plate tectonics
causes a change in texture, structure,
or composition of a rock.
Regional Metamorphism
Metamorphic Rock Groups
• Foliated: minerals within the rock
arranged in bands or planes
a) Banding- alternating bands of light and
dark minerals
b) Schistocity- minerals have grown
parallel planes in rock
c) Rock Cleavage- looks like a rock can
break into plates
HEAT
Minerals in
random order
Foliation
Realigned
minerals in
bands
HEAT
Foliated Metamorphic Rocks
Banding
Schistocity
Rock Cleavage
Identifying Rocks
• Observe and ask questions:
– What does the rock look like?
• Examine the grain of a section.
– What is the rock's composition?
• Determine what minerals are in it.
– Where was the rock found?
• Mountain
• Stream or river
• Volcano
• Ocean floor