3 TYPES OF ROCKS

Specific Learning Outcomes
At the end of the lesson, I will be able to:
a. I can identify and describe the three basic rock types;
b. I can describe how and define what type of environment
each of these rock types are formed;
c. I can describe how rocks are transformed from one rock
type to another through the rock cycle;
d. I can identify and describe the different geologic
processes that operate within the rock cycle.

8 ELEMENTS comprising almost 99% of the minerals making up the
Earth’s crust.

■ Approximately 85% of the Earth's crust is composed of oxygen and silicon.
Together they form the silicon oxygen tetrahedron, which is the basic building
block of silicate minerals.
■ Silicates are also termed as (common) rock forming minerals.
- ROCKS are an aggregate of minerals. A rock can be composed of a single
mineral (e.g. Quartzite is a metamorphic rock composed predominantly of Quartz)
or more commonly composed of an aggregate of two or more minerals.
Can a name of a mineral be also used as a
rock name?

Show a video of the different rock types.
3 Types of Rocks.mp4
How can we classify rocks? Would it be by
color, hardness, texture, density or other
physical properties? Is it by chemical
composition?

1. IGNEOUS ROCKS
• these are rocks that are derived from the cooling and solidification
of magma or lava
• from solidified molten rock materials, usually hard and crystalline
• rate of cooling as one of the most important factors that control
crystal size
• solidification can occur along the surface of the earth or
beneath the surface of the earth

MAGMA VS LAVA
• Magma is a molten rock material
beneath the surface of the earth.
• Lava is molten rock material extruded to
the surface of the earth through a
central vent (volcano) or as fissure
eruption.

1. Plutonic or Intrusive Rocks
 from solidified magma underneath the earth
 gradual lowering of temperature is indicated
by the movement of magma from depth to
surface
 causing slow cooling /crystallization
 Phaneritic textures
Forms large interlocking crystals from cooling
 Examples: granite, diorite, gabbro
2 TYPES OF IGNEOUS ROCKS

2. Volcanic or Extrusive Rocks
 from solidified lava at or near the surface of the earth
 fast rate of cooling/crystallization due to huge variance in the
temperature between Earth’s surface and underneath
 common textures: aphanitic, porphyritic (define groundmass vs
phenocrysts), vesicular
 Porphyritic texture: formed through two stages of crystallization where in
magma partly cooled below the surface of the earth providing time for the
large crystals to grow (phenocrysts) before it is extruded to the surface
forming the fine-grained matrix (groundmass).
 Aphanitic texture: fine-grained texture; minerals not visible to the naked
eye; relatively fast rates of cooling/ solidification prevent the formation of
large crystals.
 Vesicular texture: voids created by rapid cooling which causes air bubbles
to be trapped inside.

examples: rhyolite, andesite, basalt
pyroclastic rocks: fragmental rocks
usually associated with violent or
explosive type of eruption.
Examples tuff and pyroclastic flow
deposits (ignimbrite)

Common intrusive rocks with their extrusive
counterparts
GRANITE RHYOLITE

 Igneous rocks are also classified according to silica
content and relative amounts of K, Na, Fe, Mg and Ca.
They can be classified as felsic, intermediate, mafic and
ultramafic, practically based on presence of light and
dark colored minerals. The relatively dark minerals are
olivine, pyroxene, hornblende and biotite. The relatively
light colored minerals are plagioclases, K-feldspars,
quartz and muscovite.

FELSIC: granitic: >65% silica, generally light-
colored
INTERMEDIATE: andesitic: 55-65% silica,
generally medium colored (medium gray)
MAFIC: basaltic: 45-55% silica, usually dark
colored
ULTRAMAFIC: <45% silica, generally very
dark colored

2. SEDIMENTARY ROCKS
• these are rocks that are formed at or near the surface of the Earth
• sedimentary processes include:
1. weathering of rocks
2. erosion
3. deposition
4. compaction
5. Cementation
• Sediment are fragments of rock that have been broken down as a result of weathering

COMMON SEDIMENTARY FEATURES
1. fossil assemblages
 remains and traces of plants and animals that are preserved in rocks
2. Stratification
 stratification or layering (strata which is >1cm is called bedding and < 1cm is called
lamination):
 layering is the result of a change in grain size and composition; each layer represents a
distinct period of deposition

Photo of the Kapurpurawan Formation located at the coastal town of Burgos, Ilocos Norte, courtesy of
riderako.com. Shows series of sedimentary strata

1. Clastic sedimentary rocks
■ Inorganic land derived sedimentary rocks
■ Clastic sedimentary rocks form by weathering
processes which break down rocks into pebble, sand,
or clay particles by exposure to wind, ice, and water.
■ Compacted and cemented sediments
■ Clastic sedimentary rocks are named according to the
grain size of the sediment particles

2. Non-clastic sedimentary rocks
■ Organic or crystalline
■ Nonclastic sedimentary rocks form from chemical
reactions, chiefly in the ocean.
■ Nonclastic sedimentary rocks are named according to the
mineral present.
■ classified as evaporites (halite, gypsum and dolostone),
precipitates (limestone) and bioclastics (coal, coquina)

– Evaporites: rocks formed from the
evaporation of water leaving the
dissolved minerals to crystallize
– Precipitates: rocks formed when
minerals from a mineral supersaturated
waters start to crystallize at the bottom
of the solution
– Bioclastic: rock formed from compacted
organic matter

Bioclastic: rock formed from compacted
organic matter

Sedimentary rocks are the only type
of rocks that may contain fossils, or
evidence of past life.

METAMORPHIC ROCKS
• formed below the surface of the earth through the
process of metamorphism with the
recrystallization of minerals in rocks due to
changes in pressure and temperature conditions
• contact and regional metamorphism

1. CONTACT METAMORPHISM
■ HEAT AND REACTIVE FLUIDS as main factors: occurs when a
pre-existing rock gets in contact with magma which is the
source of heat and magmatic fluids where metamorphic
transformations occur around the contact / metamorphic
aureole of the intruding magma and the rock layers.
■ The aureole occurs on different scales depending on the sizes
of the intruding magma and the amount of water in the
intruded rocks and the reactive fluids coming from the
magma.
■ creates non-foliated metamorphic rocks
■ example: hornfels

2. REGIONAL METAMORPHISM
■ PRESSURE as main factor: occurs in areas that have
undergone considerable amount of mechanical deformation
and chemical recrystallization
■ occurs in a regional/large scale
■ creates foliated metamorphic rocks
■ examples: schist, gneiss
■ non-foliated rocks like marble also form through regional
metamorphism, where pressure is not intense, far from the
main geologic event

Concept Mapping – Types of Rocks
Each group will fill up the chart which correspond to the list of words provided to choose from. When done, the
group leaders will present their work to class.

VIDEO SUMMARY
■Igneous Rocks.mp4
■Sedimentary Rocks.mp4
■Metamorphic Rocks.mp4

Evaluation (20 mins)
1 whole sheet of paper

1. How does a vesicular texture in a volcanic rock develop?
2. How do clastic rocks differ from non-clastic rocks in terms of process
of formation?
3. Explain how the physical features of sediments change during
transport.
4. Differentiate between a foliated and non-foliated rock.
5. What do butterflies and metamorphic rocks have in common?
6. Heat is a major agent in metamorphism and igneous rock formation,
but not in sedimentary rocks. Why?
7. Does every rock go through the complete rock cycle, i.e. changing
from igneous to sedimentary rock to metamorphic then back to
igneous rocks? Explain.

Homework to be submitted on next meeting on a 1
whole sheet of paper. Each student will research on 3
rocks (one for each rock type).
Include in the discussion the following:
1. common environment of formation
2. common textures
3. common use of the rock

3 TYPES OF ROCKS

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