Rocks are naturally occurring mixtures of minerals, mineraloids, or organic matter that are divided into three main types - igneous, sedimentary, and metamorphic - based on their formation process. Rocks are continually changed over time through the rock cycle as they are weathered, eroded, melted, cooled, cemented, and subjected to heat and pressure, allowing them to transition between the three rock types. The composition and origins of rocks, such as whether they formed from magma, sediments, or changed forms due to heat and pressure, are used to classify the different types of rocks.

2. Wh 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 mineral?
• 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

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

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

12. ***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?

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

14. ORIGIN— FROM WHERE ROCKS
ARE FORMED
• Below ground = from magma (intrusive igneous rock)
• Usually have LARGE crystal grains

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

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

18. Peridotite: Intrusive or
Extrusive? Why?

19. Granite: Intrusive or
Extrusive? Why?

20. COMPOSITION— WHAT KIND OF SUBSTANCES THE
ROCKS ARE MADE OF

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

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

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

25. DIORITE

26. BASALT

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

28. • 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.

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

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

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

32. 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

33. 3 Types of Sedimentary
Rocks:
• Clastic (also called Detrial)—made of
broken pieces of other rocks

34. 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:

35. • 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 fo
r full size (66K JPG)
Courtesy of Martin Miller, University of Oregon

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

37. • 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

38. 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.

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

40. 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

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

42. 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)