1. Module 3: Rocks
Prepared by: Engr. Ariel S. Motas
Engr. Andreana Amor M. Gulay

2. INTRODUCTION
• Rocks are formed from an aggregation of one or
more minerals and other substances that are
cohered into a solid structure. They are classified
into three main groups based on how they are
formed. They can either be igneous, sedimentary,
or metamorphic.
Abundance of rock types by percentage
https://www.clearias.com/up/percent

3. CLASSIFICATION OF ROCKS
1. Igneous Rocks
- is formed by the crystallization of molten magma.
2. Sedimentary rock
- formed from the weathered products of preexisting rocks that have
been transported, deposited, compacted, and cemented.
3. Metamorphic rock
- formed by the alteration of pre-existing rock deep within Earth (but
still in the solid state) by heat, pressure, and/or chemically active
fluids.

4. IGNEOUS ROCKS
- from the Latin word ignis for “Fire”.
• Magma is molten material that forms deep beneath the
Earth’s surface.
• Lava is magma that reaches the surface.
• Types of Igneous Rocks:
> Intrusive/Plutonic Rocks
- cools slowly beaneath the Earth surface and are
created by magma
- have very large crystals (coarse-grained)
> Extrusive/Volcanic Rocks
- formed when lava hardens.
- crystals are very small (fine-grained) since the
cooling process is fast.

5. Igneous rocks are classified based on:
1. Texture
• Phaneritic – coarse grained texture
• Aphanitic – fine grained texture
• Porphyritic – magma partly cooled below the surface of the Earth, giving time
for the large crystals to grow (phenocrysts) before it is extruded to
the surface forming the fine-grained groundmass.
• Glassy – non-ordered solid from rapid quenching
• Pyroclastic – composite of ejected fragments
• Vesicular – voids created by rapid cooling which causes air bubbles to be
trapped inside.

6. Aphanitic Texture Vesicular Texture
Porphyritic Texture Glassy Texture

7. Igneous rocks are classified based on:
2. Composition
• Felsic – also called granitic. It contains less than 65% silica and it is
lightly colored.
• Intermediate – also called andesitic. It contains 55 -65% silica and
generally medium colored (gray)
• Mafic – also called basaltic. It contains 45 – 55% silica and generally dark
colored.
• Ultramafic – it contains less than 45% silica and generally very dark
colored. It is composed mainly of olivine and pyroxene which are major
constituents of upper mantle.

8. Some
Igneous
rocks based
on its texture
and
composition

9. FORMATION OF SEDIMENTARY ROCKS
- “Sediment” is weathered pieces of Earth elements.
1. Weathering is a process in which rocks are broken down by water, air, and
living things.
2. Erosion involves the weathering and the removal of rock
3. Deposition occurs when an agent of erosion—water, wind, ice, or
gravity—loses energy and drops sediments.
4. Lithification process by which the sediments are transformed into solid
sedimentary rocks

10. LITHIFICATION
• Compaction – as piles of sediments accumulate, the materials below are
compacted by the weight of the overlying layers. As the grains are pressed,
pore space is greatly minimized, reducing the volume. Shale is an example
of fine-grained sedimentary rock that is formed through compaction.
• Cementation – the water that seeps through pore space between particles
may contain cementing materials. Through this time, the cement settles
into the sediments grains, filling the open spaces, and then binds the
particles together. Common cements include calcite, silica (quartz) and
iron oxide.

11. FEATURES OF SEDIMENTARY ROCKS
By learning the formation of the sedimentary rocks, you may already have the idea of its distinctive features.
 Strata – also known as rock layers.
This is the layer by layer of sediments
that accumulated which can carry
with them the records of the nature
of the environment at the time the
sediments are deposited. This is the
particular importance of sedimentary
rocks to Earth’s history.
 Fossils are only found on sedimentary
rocks. This is remains and traces of
plants and animals that are preserved
in rocks.

12. TYPES OF SEDIMENTARY ROCKS
1. Clastic sedimentary rocks - also known as detrimental or terrigenous
sedimentary rocks. These rocks form from the accumulation and lithification
of sediments derived from the breakdown of pre-existing rocks. They are
further classified according to dominant grain size.
2. Non-clastic Sedimentary rocks – also known as chemical or biochemical
sedimentary rocks. These rocks are derived from sediments that precipitated
from concentrated solutions (e.g. seawater) or from the accumulation of
biologic or organic material (e.g. shells, plant material).
Clastic Non-clastic

13. METAMORPHIC ROCKS
- forms from pre-existing rocks: either methamorphic, igneous, sedimentary
METAMORPHIC AGENTS
Metamorphic agents are the factors that are cause of changes or
transformation of parent rocks.
1. Heat - The most important agent of metamorphism is heat that may come
from magma rising from below. The parent rick is baked by the magma.
Another source of heat when rocks are formed at the surface of Earth are
transplanted to greater depth. As the rocks go deeper, the temperature
increases. The heat here caused chemical reactions that results in
recrystallization of existing minerals and/or formation of new
minerals.

14. METAMORPHIC ROCKS
- forms from pre-existing rocks: either methamorphic, igneous, sedimentary
METAMORPHIC AGENTS
2. Pressure - Like temperature, pressure increases with depth. Pressure causes
the spaces between the mineral grains in the buried rocks to close, producing
more compact rock with higher density. At greater depth, minerals may
recrystallize into new minerals.
3. Chemically-active fluids - These
chemically active fluids include water, carbon
dioxide and other volatile materials. They act
as a catalyst to promote crystallization by
enhancing ion migrations that may change
the composition of the rocks.

15. METAMORPHISM
- transformation of one rock type into another
TWO TYPES OF METAMORPHISM
1. Regional – due to changes in pressure and temperature over large region of
the crust
2. Contact – mainly by heat due to contact with magma
- changes are driven by a rise in temperature

16. CLASSIFICATION OF METAMORPHIC ROCKS
2. Non-foliated Metamorphic Rock
- Does not have a banded texture
- Occurs where pressure is not intense, far
from the main geologic event.
- Example is marble
Metamorphic grade increases (from slate to gneiss) as
pressure increases.
1. Foliated Metamorphic Rock
- Has a banded or layered appearance

17. Common metamorphic rocks have
economic value. Slate is used for
roof, floor, tile and chalkboard.
Marble is popular building stone
because of its color (pink, gray, and
green, black) and relative surface,
White marble is used for statues
and monuments.

18. ROCK
CYCLE

19. 2. Nonfoliated Metamorphic Rock -