Rocks are naturally occurring mixtures that can be divided into three main types - igneous, sedimentary, and metamorphic - based on their formation process. Igneous rocks form from cooling magma or lava. Sedimentary rocks form through the compaction or cementation of sediments. Metamorphic rocks form from changes to existing rocks through heat, pressure, and other processes in the Earth. Rocks continually change between these types through the rock cycle as they are weathered, eroded, melted, cooled, and compacted over time.

2. W h a t is a R o c k ?
• Naturally-occurring mixtures
of minerals, mineraloids, glass
or organic matter.

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

4. What is the difference between a
rock and a m ineral?
• Rocks are made up of ONE or
MORE minerals.

5. Once a rock is formed, does it
stay the same rock forever?
• NO!

6. • 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

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

11. • No set path a rock takes to become
another kind of rock

12. Weathering, Erosion,
Compaction,
Cementation
Recrystallization
Weathering, Erosion,
Compaction,
Cementation
Recrystallization
Melting,
Solidification Melting,
Solidification

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

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

16. • “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

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

19. Some have large & small crystals
(called porphyritic)

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

21. Peridotite: Intrusive or
Extrusive? Why?

22. Granite: Intrusive or
Extrusive? Why?

23. Porphyry: Intrusive or
Extrusive? Why?

24. Obsidian: Intrusive or
Extrusive? Why?

25. COMPOSITION— What kind of
substances the rocks are made of

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

27. Granitic Igneous Rocks—made
from magma/lava high in
silica and oxygen. Rocks are
light-colored.

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

29. Diorite

30. Basalt

31. Granite

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

33. • 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.

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

35. • The heavy sediments press down on
the layers beneath (compaction)

36. • Dissolved minerals flow between the
particles and cement them together
(cementation)

37. 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

38. 3 Types of Sedimentary
Rocks:
• Clastic (also called Detrial)—made of
broken pieces of other rocks

39. 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:

40. • Chemical—minerals dissolved in
lakes, seas, or underground
water
3 Types of Sedimentary
Rocks:
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

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

42. • 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

43. 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.

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

59. 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)