1. Rocks:
Sedimentary
Igneous
Metamorphic
Keepers of Earth’s History 1

2. Goals for understanding rocks:
Understand the importance of the rock cycle
Describe composition and texture characteristics
of igneous, sedimentary and metamorphic rocks
Understand the sedimentary rock cycle and
how it relates to the creation of sedimentary rocks
Describe a sedimentary facies and its importance
when deciphering geologic history
Explain the various geologic environments
associated with each major rock type 2

3. Granite What’s in your rock?: Hornblende Orthoclase Quartz
aggregates of minerals
Biological material
Fossil fragments
Plant material 3

4. Understanding rocks is the basic foundation of
knowledge for earth scientists and materials that
make up the earth.
Every rock “speaks” to the observer and gives
clues about where and how it was formed.
Rocks are divided into 3 major groups:
Igneous
formed from solidifying hot molten
rock (magma)
Sedimentary
formed on the surface of the earth from
weathering processes
Metamorphic
pre-existing rocks are subjected to
various pressure and temperature
relationships 4

5. All rocks are identified based on their texture and composition.
How does an earth scientist distinguish between
the three rock types (Ig, Seed, and Met)?
Texture:
the appearance of the rock
size, shape, and arrangement of mineral grains.
Composition (mineral assemblages)
types and relative proportions of minerals
making up a rock
composition, mineral make-up, chemistry--all
indicators of a rock’s composition
All rocks are identified based on their
texture and composition. 5

6. 6
The Rock Cycle
The Sedimentary Cycle

7. where the earth’s internal forces meet
The Rock Cycle:
where the earth’s internal forces meet
the earth’s external forces (at the earth’s
surface) 7
Earth’s internal forces
Earth’s external forces
the hydrosphere (HC)
atmosphere
erosion (wind, water, ice)
biosphere activities
moving continents (PT)
earthquakes
elevation of mountains
volcanic eruptions
Produce a continuous cycle of rising mountains only to be
weathered down and uplifted repeatedly. As a result, igneous
sedimentary, and metamorphic rocks are created.

8. I Earth Science, especially the rock cycle !!!!!!!!!!!!! 8
Discuss with a friend:
Briefly identify each rock group and
its geologic environment.
2. Draw the rock cycle, and explain how the
rock cycle works to your neighbor.
3. Why is the rock cycle a “cycle”???
I will get an A on my exams and quizzes.

9. Geology – Chapter 3 – Igneous Rocks9

10. Magma Extrusive - igneous rocks – above the earth’s surface
the parent material for igneous rocks (if not all rock groups)
typical temperature 1,200oC (2,200oF)
forms about 250 km or 150 miles below the earth’s surface
Extrusive - igneous rocks – above the earth’s surface
volcanic rocks
lava flows
Example – Hawaiian Volcanoes
Intrusive - igneous rocks – below the earth’s surface
plutonic rocks
large granite mountains
Example – Sierra Nevada Mountain Range 10
Grain size determines if the ig rock is extrusive or
intrusive. Magma determines the rock’s composition.

11. surface (fine-grained) surface (coarse-grained)
When observing “frozen magma” (an igneous rock), how
does a geologist know if the rock is an Extrusive or
Intrusive igneous rock?
checking the crystal size - Does the rock contain visible
crystals, or are crystals non-existent?
Igneous Rock Textures
Factors that affect crystal size in an igneous rock:
The rate at which magma cools
slow cooling – visible minerals
rapid cooling – non-visible minerals
visible minerals
slow cooling magma
intrusive ig rock
non-visible minerals
rapid cooling magma
extrusive ig rock
Cooled above the
surface (fine-grained)
Cooled below the
surface (coarse-grained) 11

12. Volcanic (Extrusive) Igneous Rock Textures
obsidian
glassy texture: not crystalline, but glassy
lava cools very rapidly
basalt
aphanitic texture: extremely small
crystals that cannot be observed
with the naked eye
porphyritic texture:
bimodal grain size, where
two distinct crystal sizes
exist at the same time
Pumice
vesicular texture: Dissolved gases
rise within the lava and are released.
Released gasses “bubble” out of the
lava, leaving “holes” or vesicles. 12

13. Plutonic (Intrusive) Igneous Rock Textures
phaneritic texture: Magma below
the surface has time to cool, forming
visible mineral grains. Grains are
usually equidimensional (same size).
granite
pegmatitic texture: Gases are
left over in late stage cooling that
facilitate larger crystal growth.
Crystals are greater than 2 cm.
Grain boundaries are
interlocking. Grains
are less than 2 cm. 13

14. Composition of Igneous Rocks 14
How much silica (SiO2) is in your igneous rock?
Felsic compositions (feldspar + silica)
light-colored igneous rocks
common minerals: feldspar and quartz
70% SiO2
Intermediate compositions:
mixture of felsic and mafic minerals
about 60% silica (SiO2)
Mafic compositions (magnesium + iron)
dark-colored igneous rocks
common minerals: olivine and pyroxene
50% SiO2
ultramafic: composed entirely of olivine and pyroxene
and less than 50% silica (SiO2)

15. How are igneous rocks classified? Using their TEXTURE and COMPOSITION
Igneous rocks are classified based on TEXTURE and
COMPOSITION. 15
COMPOSITION
Felsic (light color)
70% silica
Intermediate color
60% silica
Mafic (dark color)
50% silica
phaneritic
COARSE
Granite
Diorite
Gabbro
TEXTURE
aphanitic
FINE
Rhyolite
Andesite
Basalt
Igneous rocks have the same chemistry but
different textural characteristics due to the type
of geologic environment (cools quickly or slowly).

16. Low viscosity High viscosity
Lava flows versus pyroclastic (fire-particles) eruptions
(depends of silica (SiO2) concentration)
Lava flows
Pyroclastic flow
Low SiO2
High SiO2
Low viscosity
gas bubbles escape easily
High viscosity
gas bubbles are trapped
Example: basaltic flows
that are vesicular
Example: very explosive
eruptions, shattering magma
into hot fragments (tephra)
Tephra range in size from volcanic
dust to car-sized rocks. 16

17. I Earth Science, especially igneous rocks.
What is the difference between extrusive
and intrusive igneous rocks?
2. How can one tell the difference between
an extrusive and intrusive rock texture?
3. The composition of a mafic ig rock is….
The composition of a felsic ig rock is ….
4. A fine-grained, light-colored ig rock is
called a ………………….
I will get an A on my exams and quizzes. 17

18. Sedimentary Rocks 18

19. How is a sedimentary rock formed??? 19
Why is the earth’s surface 75% sedimentary rocks?
erosion
Pre-existing
Rock
sediment
water, wind,
ice
breaks down
pre-existing rock
Rivers
Deposited
transported
Lakes
lithified
compacted
cemented
Sedimentary
Rock

20. I sedimentary rock classification. Discuss with a friend:
Describe the sedimentary rock cycle.
I will get an A on my exams and quizzes. 20

21. Erosional processes – later (Chapter 4) 21
Erosional processes – later (Chapter 4)
Sediments are separated into 3 broad categories:
Clastic sediments:
inorganic grains or mineral fragments ranging in
size from boulders to clay particles (flour size)
Chemical sediment:
formed by the precipitation of minerals dissolved
in lakes, rivers, or seawater environments
Biogenic (bioclastic) sediment:
sediment composed of animal and plant remains or
material precipitated by biological processes
To be a sedimentary rock, it must be lithified.

22. Lithification: processes by which sediment is
transformed into sedimentary rock
Sediment can be lithified in three common processes:
Compaction: Overlying weight of the sediment “squeezes”
and compresses pore spaces, which pushes particles together.
A. loose, unconsolidated sediment with
abundant pore space
B. compacted, compressed sediment with
reduced pore space A B
Cementation: Pore water is expelled from voids, and rising
water carries iron, calcium carbonate, and silica which precipitates
as geological glue (cement) holding the grains together.
Grains are cemented together by three
types of cements:
iron cement
calcium carbonate cement
silica cement 22

23. Grain boundaries convert compositions, “cementing”
Lithification processes
Recrystallization: Overlying pressure causes less stable
minerals to convert to more stable minerals, producing new
substances that cement pre-existing grains.
Grain boundaries convert
to more stable mineral
compositions, “cementing”
grains together.
Overlying pressure 23

24. Clastic Sediment: conglomerate sandstone siltstone shale 24 lithified
gravel sediment ranging
from pea-sized to larger
conglomerate
lithified
sand-sized particles (fine to coarse
sandpaper)
sandstone
lithified
finer particles – size of table salt
siltstone
finest sedimentary
particles (flour-size)
lithified
shale 24

25. Clastic (inorganic-detrital)
Rocks are composed of particles or grains.
Rock name is dependent on grain size.
Conglomerate
Breccia
Decreasing grain size
sandstone
2+ mm
Arkosic SS
Siltstone
2 mm
Shale
1/16 mm
Claystone
1/256 mm 25

26. Chemical Sediments and Sedimentary Rocks
Chemical Sediment: sediment formed by the precipitation
of minerals dissolved in a lake, river, or seawater
All surface water and groundwater contain
dissolved ions (chemicals), creating a venue for
precipitation of chemical sediment.
Precipitation of chemical rocks takes place in two ways:
Plants and animals alter the chemical balance
of the water body (lake, ocean).
Increasing amounts of calcium carbonate
cause precipitation of limestone.
evaporation of chemically saturated water
bodies 26

27. Evaporation of chemically saturated water creates
a chemical sedimentary rock (evaporite).
Na+
Na+
Cl-
a lake containing sodium (Na+)
and chlorine (Cl-)--free ions
Cl-
Cl-
Na+
Na+
Cl-
Evaporation
Lake water is evaporated,
concentrating sodium and
chloride ions (saturation).
Sodium and chlorine combine
to form halite (table salt).
NaCl 27

28. The Great Salt Lake, Utah
(evaporite halite) 28
As lake becomes saturated,
density of water increases.
Utah

29. Chemical – sedimentary rocks that have been
precipitated or are the result of evaporation
Gypsum – evaporite CaSO4
Halite – evaporite
NaCl
Limestone--
precipitated
calcium carbonate 29

30. Biogenic Sediments and Biogenic Rocks:
Biogenic sediment is composed of organic remains of plants and
animals (bioclastic rocks).
shell, bones, teeth, plant fragments, wood, roots 30
Common Biogenic Rocks:
Limestone
most abundant biogenic sedimentary rock
composed of calcium carbonate CaCO3(calcite, dolostone,
aragonite)
lithified shells, skeletal material
Chert
composed of silica SiO2
precipitated silica shells (made by sea animals) that protect
microscopic sea animals – Animals die, and silica shells
sink, creating layers of chert beds on the ocean floor.
“When the animal dies, it loses the chert off its back.”

31. Common Biogenic Rocks 31 Peat to Coal Peat Anthracite coal
accumulated remains of terrestrial plants
with time and pressure ---- peat
continued pressure and lithification coal
lithification
Peat
Increasing pressure
metamorphism
Anthracite coal
Bituminous coal

32. Biogenic (bio-clastic) rocks –
result from animal and plant secretions -- The term
“clastic” indicates that these rocks contain fossils or
parts of plants, shells, compacted plant material
Animal parts
Cemented shell fragments
Fossil Limestone
Microscopic fossils
Coquina 32
Chalk

33. What do sedimentary rocks tell the earth scientist?
These rock “layers” were
deposited one layer at a
time and lithified.
The banded appearance
is known as bedding or
groups of layers called strata.
The boundary between
each stratum is called a
bedding surface.
Bedding surface
bedding
strata
By observing the sedimentary rock type (clastic, chemical,
biogenic) and depositional patterns, an earth scientist can
decipher the geologic history – like reading pages in a book. 33

34. 34 Patterns of Sedimentary Depositional Environments
(What characteristic pattern is left on the bedding surface?) 34
Water ripple marks left their imprint
(oscillation ripple marks).
present day mud cracks
Present day mud cracks
are typical of wet/dry
seasonal lake beds.
What interpretation can
be hypothesized about
the preserved mud cracks?
“fossilized” preserved
mud cracks

35. Sedimentary facies 35 changes in the character of
sediment from one environment
to another 35
regolith
beach sand
continental shelf
offshore
transition zone
offshore deep
ocean sediment

36. I sedimentary rock classification. 36 Discuss with a friend:
Describe at least 2 characteristics of
each sedimentary rock classification
(clastic, biogenic, chemical).
Give a rock example for each classification.
3. What is a sedimentary facies? What
importance do they have to an earth scientist?
I will get an A on my exams and quizzes.

37. Metamorphic Rocks 37

38. What is “metamorphism?”
meta (change) morphism (form)
transformation of pre-existing
rock to a metamorphic rock
through pressure and
temperature relationships
All changes take place through
solid state transformation. 38

39. takes place around 150oC (Temperature)
Types of Metamorphism
takes place around 150oC (Temperature)
typically at depths of 5 km below the
earth’s surface (Pressure)
At this temperature and pressure, new minerals
are formed – changed from one mineral to
another. 39

40. I metamorphic rocks. Discuss with a friend:
How do you define metamorphism? – Be
specific.
What two major factors are necessary
for pre-existing rocks to become
metamorphosed?
3. Where does metamorphism typically
take place within the earth?
I will get an A on my exams and quizzes. 40

41. Low-grade Metamorphism
between 5-15 km below the earth’s
surface
temperatures up to 400oC
common low-grade minerals
quartz, chlorite, muscovite 41
Chlorite
Muscovite
Quartz

42. High-grade metamorphism 15 km below the surface to the melting42
High-grade metamorphism
15 km below the surface to the melting
point (when melting occurs)
temperatures greater than 400oC
common high-grade minerals
garnet, kyanite, sillimanite
kyanite
Garnet
sillimanite

43. Migmatite How do fluids enhance metamorphism?
Minerals dissolve – reprecipitated in the rock.
Fluids speed up chemical reactions – reduce
mineral melting points, creating “migmatites.”
Igneous rock material
Migmatite
Metamorphic rock
Melting occurs from lowered
melting points, creating small pockets of igneous
rocks surrounded by
metamorphic rocks. 43

44. 2 Common types of metamorphism
contact metamorphism
regional metamorphism 44

45. What is contact metamorphism?
magma “contacts” solid rock –
heat is transferred into overlying
rocks through conduction – changing
the pre-existing rock it intruded
high heat/low pressure
localized metamorphism
“fast-acting,” like touching a
hot frying pan 45

46. Country rock (surrounding) is baked from conduction.46

47. What is regional metamorphism?
Pre-existing rock is subjected to intense
stresses and strains (deformation) usually
from the forces of mountain building.
high heat/high pressure
very widespread geographically
like experiencing a slow sunburn 47

48. Mountain building
widespread belts 48

49. I the different ways to create Metamorphism. Discuss with a friend:
Describe the conditions necessary for each
type of metamorphism:
contact metamorphism
regional metamorphism
I will get an A on my exams and quizzes. 49

50. Heat: What does each metamorphic process have in common?
provides the energy to cause
recrystallization of pre-existing
minerals into “new” types of minerals
Heat sources:
contact with hot magma – heat penetrates
overlying rocks (conduction)
geothermal gradient – heat increases with
depth – rocks are hotter when buried 50

51. 51 Geothermal Gradient Steep gradient Temperature increases
as depth increases.
Large thermal gradient
is at the surface.
Gradient decreases
after 1000 km depth.
Steep gradient
1000
2000
3000
4000 51

52. Pressure – increases with depth,52
Pressure – increases with depth,
various types of pressure rearrange
minerals – minerals compact or elongate
Confining pressure
Differential pressure

53. How does one know how much metamorphism has taken place in a rock? 53
How does one know how much metamorphism
has taken place in a rock?
reflected in the rock’s texture
Metamorphosed – mineral
grains are in a preferred
direction -- FOLIATION
Not Metamorphosed

54. I to metamorphose. 54 Discuss with a friend:
Describe two heat sources associated with
metamorphism.
Define the differences between confining
and differential pressures.
3. Draw a diagram that shows mineral
orientation due to confining and
differential type pressures.
I will get an A on my exams and quizzes.

55. 55

56. I metamorphic rocks. Discuss with a friend:
Describe the metamorphic rock texture
that is foliated.
How does a geologist know if a rock
has been metamorphosed?
3. Now, knowing what the three classes of rocks
are, draw the rock cycle in detail.
I will get an A on my exams and quizzes. 56