Download Rocks - Choteau Schools

Rocks
Chapter 4
What is a rock?

Rock

Mixture of minerals, rock
fragments, volcanic glass, organic
material, or other natural
materials.
What is a rock?

Rock Cycle

Cycle that demonstrates the three
types of rock and the processes
that create and change them.
What is a rock?

Matter and
the Rock
Cycle

Changes that occur in the rock
cycle never create or destroy
matter.

Elements that form the rocks are
simply redistributed.
Formation of Igneous Rocks

Igneous Rocks

Form when magma cools and
hardens.
Formation of Igneous Rocks

Magma

Forms when heat and pressure
in the interior of the earth melt
rock.



Temps of magma range from 650
to 1200 degrees Celsius
Because magma is less dense than
surrounding solid rock it is forced
upward.
Magma that has erupted to the
surface of the earth is called
lava.
Formation of Igneous Rocks

Intrusive Rocks

Igneous rocks that form
beneath the surface of the
earth.

Cool very slowly which results in
large mineral grains (coarsegrained).
Formation of Igneous Rocks

Extrusive Rocks

Form when lava cools on the
surface of the earth.

Cool rapidly resulting in small
mineral grains (fine-grained).

Volcanic glass is a type of extrusive
igneous rock with no to few mineral
grains

Very rapid cooling
Classifying Igneous Rocks

Classification


Classified as intrusive or
extrusive
Classified into three families
based on composition of magma
from which they formed.



Basaltic
Granitic
Andesitic
Classifying Igneous Rocks

Basaltic Rocks


Dark-colored, dense
Form from magma low in silica
and high in magnesium and iron

Examples: Hawaii, moon
Classifying Igneous Rocks

Granitic Rocks


Light-colored, lower density
Form from magma rich in silica
Classifying Igneous Rocks

Andesitic Rocks

Form from magmas in between
felsic (granitic) and mafic
(basaltic).
Metamorphic Rocks

Metamorphic
Rocks

Rocks that have been changed
by high temperature, high
pressure, or hot fluids.

The rock from which the
metamorphic rock formed is
called the parent rock.
Classifying Metamorphic Rocks

Classification

Classified according to mineral
composition and texture.

Foliated


Mineral grains of the rock are
arranged in parallel layers.
Nonfoliated

Mineral grains of the rock are not
arranged in layers.
Formation of Sedimentary
Rocks

Formation of
Sedimentary
Rocks

Form when sediments are pressed
and cemented together or when
minerals form from solution.

Sediments are loose materials such as
rock fragments, mineral grains, and
organics (bits of shell, etc).

Come from rock that has been eroded.
Classifying Sedimentary Rocks
Classification

Classified by the type of sediments
in the rock and how the rock
formed.



Detrital
Chemical
Organic
Detrital Sedimentary Rocks

Formation

Formed from pieces of other rock
that have been compacted or
cemented together.


When exposed to the air, water, and
wind rock is broken down through the
process of weathering.
Sediments can be moved through
erosion to new locations where they are
deposited.
Detrital Sedimentary Rocks

Compaction

As sediments are deposited, sediment
layers on top put pressure on sediment
layers below them, eventually pressing
the sediments into rock.
Detrital Sedimentary Rocks

Cementation



As water moves through rocks,
minerals are dissolved in the water.
The water carries the dissolved
minerals through cracks in rock.
These minerals (such as quartz,
calcite, or hematite) can be
deposited between pieces of
sediment, cementing them into
rock.
Detrital Sedimentary Rocks

Further
classification

Detrital sedimentary rocks are
further classified by the shape and
size of sediments that form them.
Chemical Sedimentary Rocks

Formation

Form when dissolved minerals come
out of solution.

Limestone


Calcium carbonate is dissolved in ocean water
and precipitates out as calcite, forming
limestone.
Rock Salt

Water rich in salts leave the mineral halite
when the water evaporates, forming deposits
of rock salt
Organic Sedimentary Rocks

Formation

Rocks that are made from the remains
of once living things


Fossil-rich limestone
Chalk


Consists of microscopic shells.
Coal

Formed from plant remains buried in swamps.

The plant remains are changed into coal by
microscopic organisms and pressure.