What is a Rock?

Naturally-occurring mixtures of
minerals, mineraloids, glass or organic matter.

What is a Rock?

Rocks are divided into 3 groups based on how they were formed:

IGNEOUS

SEDIMENTARY

METAMORPHIC

What is the difference between a rock and a

Rocks are made up of ONE or MORE minerals.
mineral?

Once a rock is formed, does it stay the same rock forever?

NO!


Rocks are continually changed by many processes, such as weathering, erosion, compaction, cementation, melting, and cooling

Rocks can change to and from the three types

What is the process through which rocks change?

The Rock Cycle—earth materials change back and forth among the different types of rocks


No set path a rock takes to become another kind of rock

IGNEOUS
Weathering, Erosion,
Compaction,
Cementation
Melting,
Solidification
SEDIMENTARY
Recrystallization
Melting,
Solidification
Recrystallization
Weathering, Erosion,
Compaction,
Cementation
METAMORPHIC

How are rocks redistributed?

The core, mantle, & crust are one giant rock recycling machine

***Watch the Rock Cycle by Brainpop
1.
2.
3.
What do igneous rocks form from?
What kind of rock is sandstone?
What are metamorphic rocks formed by?

How can Starbursts represent
 the Rock Cycle?
Which rock form does your stacked
Starbursts represent?

Now press your sedimentary rock in the palm of your hands for at least 2 minutes (do not twist)



What do you observe?
Which type of rock does this represent?
Teacher Demonstration


Watch as the new Starburst “rock” is melted. What do you notice?
What kind of rock is it now?


“Ignis” = Latin for “fire”

Formed from the cooling of either magma or lava

The most abundant type of rock

Classified according to their origin and composition

ORIGIN
— Where rocks are formed

Below ground = from magma (intrusive igneous rock)

Usually have LARGE crystal grains (they cooled
slowly)

Some have large & small crystals
(called porphyritic)


Above ground = from lava (extrusive igneous rock)

Usually have SMALL or NO crystals (they cooled too quickly)

Practice Classifying Igneous Rocks as intrusive or extrusive
—

Take out & classify these rocks from your kits. Examine their crystals.
Classify them (circle your choice) and tell why you did.

#5 Peridotite: Intrusive or
Extrusive? Why?

#4 Granite: Intrusive or
Extrusive? Why?

#11 Porphyry: Intrusive or
Extrusive? Why?

#12 Obsidian: Intrusive or
Extrusive? Why?

COMPOSITION
—
What kind of substances the rocks are made of

Basaltic Igneous Rocks
—made from lava/magma that is low in silica, rich in iron and magnesium. Rocks are dark- colored
.

Granitic Igneous Rocks—made from magma/lava high in silica and oxygen. Rocks are lightcolored.

Andesitic Igneous Rocks— have a composition between basaltic and granitic.

Practice Classifying Igneous Rocks according to their composition:

#1: Diorite

#8: Basalt

#4: Granite


Formed from sediments
(rock fragments, mineral grains, animal & plant remains) that are pressed or cemented together or when sediments precipitate out of a solution.



These sediments are moved by wind, water, ice or gravity.
Sedimentary rocks represent 7% of the
Earth’s crust, but they cover 70% of the Earth’s surface.

Sedimentary rocks are fossil-carrying rocks.

What turns sediments into solid rock?

Water or wind breaks down and
deposits sediment (erosion & deposition)


The heavy sediments press down on the layers beneath (compaction)


Dissolved minerals flow between the particles and cement them together
(cementation)

How were most of the sedimentary rocks in the Puget Sound area deposited?

Glaciers about 1500 years ago.

How can sedimentary layers help us understand the age of fossils?


As sedimentary rocks are deposited, they form horizontal layers
Scientists know that the layers on
top (and the fossils in the top layer) are
YOUNGER than the fossils in lower layers.

3 Types of Sedimentary
Rocks:

Clastic (also called Detrial)—made of
broken pieces of other rocks

3 Types of Sedimentary
Rocks:
Organic—remains of plants and animals are deposited in thick layers


Examples
Fossil rich limestone is made from the shells of ocean animals; used to make chalk

3 Types of Sedimentary
Rocks:

Chemical—minerals dissolved in lakes, seas, or underground water
Mineral crystals are made as the shallow water that has flooded the bottom of Death Valley evaporates.
Click on image for full size (66K JPG)
Courtesy of Martin Miller, University of Oregon

Examples

Limestone made when calcite mineral precipitates from sea water

Rock Salt— made from evaporation of sea waters




Rocks that have changed due to intense
temperature and pressure
“Meta” means “change” and morphosis means “form” in Greek
Igneous, sedimentary and other metamorphic rocks can change to become metamorphic rocks

What occurs in the Earth to change these rocks?

Pressure from overlying rock layers

High heat, but not enough to melt the rock

Rocks may be flattened or bent or atoms may be exchanged to form new minerals.


*You can think of metamorphic rocks as a squished peanut butter & jelly sandwich in your lunch.

How are metamorphic rocks classified?

Foliated—mineral grains are flattened and line up in parallel bands

Example: gneiss formed from rearrangement of minerals in granite into bands

How are metamorphic rocks classified?

Non-Foliated—No bands are formed

Example: marble formed from limestone

Where do metamorphic rocks usually form?






Where magma intrudes relatively cool rock
Near colliding plates (near mountain ranges)
Places that are covered miles thick with other rock causing pressure
When hot water intrudes rock
Where a meteorite strikes Earth
(rare)
Where lightning bolts strike rocks
(rare)