Download Types of Rocks

Types of Rocks
• There are three main types of rocks:
1.
Igneous - formed when molten rock cools.
2.
Sedimentary – formed by the “cementing
together” of small grains of sediment.
3.
Metamorphic – rocks changed by the effect of
heat and pressure.
Here is another version of the Rock Cycle
Igneous Rocks
•
These are rocks formed by the cooling of molten
rock (magma.)
Magma
cools and
solidifies
forming
igneous
rocks
volcano
magma
Granite
• Light-colored, coarsegrained, no pattern
• Mostly quartz,
feldspar, mica, and
hornblende
• Often used for
buildings and
monuments
Basalt
• Dark-colored, finegrained, extrusive
• Formed where lava
erupted onto surface
• Most widespread igneous
rocks
• Found locally in the
Palisades along west
shore of Hudson River,
Connecticut River valley
Gabbro
• Dark-colored, coarsegrained intrusive
• Similar composition to
basalt—plagioclase
feldspar with some
pyroxene and olivine
Obsidian
• Natural volcanic glass
• Forms when lava cools
very quickly
• Usually dark, but small
pieces may be clear
• Fractures along curved
(conchoidal) surface
• Used as spear and
arrow points, knives
Pumice and other igneous rocks
• Light colored, frothy
(many air spaces)
• Same minerals as in
granite, but finer in
grain size
Sedimentary Rocks
•
Getting older
Sedimentary Rocks are rocks
formed when particles of sediment
build up and are “cemented
together” by the effect of pressure
and minerals.
Fragments washed to the sea
Rocks are broken
up by the action
of weather
sea
Sedimentary
rocks
Sedimentary Rocks
Sedimentary rocks may be made of rock fragments—
sediments—or by chemical reactions. The classification of
sediments is shown below.
Sedimentary Rocks




Sedimentary rock is formed by erosion
Sediments are moved from
one place to another
Sediments are deposited in
layers, with the older ones
on the bottom
The layers become compacted
and cemented together
http://www.fi.edu/fellows/payton/rocks/create/sediment.htm
Importance of
Sedimentary Rocks
Bauxite: ore of aluminum
Sedimentary Rock

Sedimentary Rocks are formed at or near
the Earth’s surface

No heat and pressure involved

Strata – layers of rock

Stratification – the process in
which sedimentary rocks are
arranged in layers
Sedimentary Rock
Clastic – made of fragments of rock
cemented together with calcite or quartz
Breccia is a term most
often used for clastic
sedimentary rocks that are
composed of large angular
fragments (over two
millimeters in diameter).
The spaces between the
large angular fragments
can be filled with a matrix
of smaller particles or a
mineral cement that binds
the rock together.
Sedimentary Rock
Chemical sedimentary – minerals crystallize
out of solution to become rock
Limestone is a sedimentary
rock composed primarily of
calcium carbonate (CaCO3) in
the form of the mineral calcite.
It most commonly forms in
clear, warm, shallow marine
waters.
It is usually an organic
sedimentary rock that forms
from the accumulation of
shell, coral, algal and fecal
debris.
Sedimentary Rock
Organic sedimentary – remains of plants and
animals
Coal is an organic
sedimentary rock that
forms from the
accumulation and
preservation of plant
materials, usually in a
swamp environment.
Coal is a combustible
rock and along with oil
and natural gas it is one
of the three most
important fossil fuels.
Conglomerate
Breccia (“Bretcha”)
Sandstone
Coquina
Metamorphic Rocks
•
•
Metamorphic rocks are formed by the effect of
heat and pressure on existing rocks.
This can greatly affect the hardness, texture or
layer patterns of the rocks.
Pressure from surface
rocks
metamorphic
rock
Magma
heat
forming
here
Metamorphic Rock
 Meaning to change shape
 Changes with temperature
and pressure, but remains
solid
 Usually takes place deep in
the Earth
http://www.fi.edu/fellows/payton/rocks/create/metamorph.htm
Hornfels
Foliated MM Rocks
slate
phyllite
schist
gneiss
MM
MM Rocks
Rocks that
that could
could form
form as
as aa shale
shale (sedimentary)
(sedimentary) parent
parent rock
rock is
is
exposed to increasing directed pressure and temperature
Migmatite
Migmatite- note blobs of quartz