A comprehensive lesson on rocks and their types including the rock cycle and the importance of rocks

1. OCCLUDED PFOF. 1

2. OCCLUDED PFOF. 2

3. 3OCCLUDED PFOF.

4. • Rocks are one of the solid materials of
the lithosphere(earth) which is made up
of mineral aggregate. The solid materials
or component of the earth are termed as
rocks: they are the chemical combination
of minerals( natural occurring element
such as oxygen, hydrogen, calcium etc).
• Examples of rocks include, granite, coal,
slate, sand, limestone etc.
• Basically, there are three types of rocks
which are based on their mode of
formation and they included,
sedimentary rocks, igneous rocks and
metamorphic rocks.
ROCKS
PICTURES OF SOME ROCKS

5. TYPES OF ROCKS
There are three main types of rocks namely,
SEDIMENTARY ROCKS
IGNEOUS ROCKS
METAMORPHIC ROCKS (SIM)
IGNEOUS ROCKS
Igneous rocks are formed from the cooling, solidification and crystallization of
molten materials(magma) within the earth crust or on the surface of the earth.
They are also known as volcanic rocks. Igneous rocks.
Igneous (fire) rocks are formed through intense heat deep within the earth that
result in transforming rocks into liquid and semi liquid state (magma). When
molten materials undergo intense heat and pressure within the earth crust, they
are forced to rise through a crack or a join or a fault. It may get to the earth’s
surface depending on the pressure amounted by the magma through the rock
crevices.
producing basically three types of igneous rocks
.
Plutonic Rocks – deep within the earth
Hypabyssal Rocks – just beneath the earth surface
Extrusive Rocks – on the surface of the earth
The magma which finds it way unto the earth surface is known as lava. Examples
of igneous rock include, gabbro, diorite, granite, dolerite
Igneous rocks produce the following characteristics:
They are hard, compact and resistant rocks
They are massive rocks without pores
They are crystalize in nature
CHEMICAL COMPOSITION OF IGNEOUS ROCKS
An igneous rock of 65% and more silica content is an acid igneous rock whiles
basic igneous rocks have less silica content .eg. basalt
OCCLUDED PFOF. 5

6. OCCLUDED PFOF. 6

7. TYPES OF IGNEOUS ROCKS
• PLUTONIC ROCKS
• They are formed from the
solidification of molten rocks
deep within the earth crust.
• The process of solidification is
very slow due to limited air for
cooling within the earth. This
result in formation of large
crystalline rocks including
granite, gabbro and diorite.
7

8. OCCLUDED PFOF. 8

9. HYPABYSAL ROCKS
These are rocks that are formed when magma cools and solidifies
just beneath the earth surface, thus along the lines of weakness
and cracks at shallow depths. Cooling is moderate leading to
medium crystal formation. Examples include, dolerite and
porphyry.
EXTRUSIVE ROCKS
They are formed from the cooling and solidification of
molten rocks as they erupt unto the earth’s surface. A
solidified magma on the earth’s surface is known as
lava. Extrusive rocks solidifies faster and produces
highly crystalline rocks which are glassy and has fine
texture.
Examples include: basalt, andesite and rhyolite.
MOLTEN MAGMA AT ROCK CREVICES,
THE YELLOW RING ZONE INDICATION
Fig. 1. ERUPTING MAGMA Fig. 2. LAVA FORMATIONOCCLUDED PFOF. 9

10.  Sedimentary rocks are formed from the lithification process of
deposition, compaction, cementation and crystallization of debris. Thus
the accumulation other rock fragment, precipitates of water solution and
remains of plant and animals in water or on land. Debris move from
higher elevation by agents of denudation and the direct pull of gravity.
 They are characterized by the following;
 They have bedding planes separating their layers
 They are stratified
 They less compact and porous
 They may contain fossils: remains of plants and animals
 Examples of sedimentary rocks included, sandstone, mudstone, clay, coal
and limestone
 CLASSIFICATION OF SEDIMENTARY ROCKS
The litification process of sedimentary rock formation leads to
three main groups of sedimentary rocks and they are;
 Mechanically formed sedimentary rocks – agents of denudation
 Organically formed sedimentary rocks – remains of living organisms
 Chemically formed sedimentary rocks – precipitation of chemicals in
solutions Picture showing sedimentary rocks in layers
OCCLUDED PFOF. 10

12. OCCLUDED PFOF. 12

13. • MECHANICALLY FORMED SEDIMENTARY ROCKS
• These are formed by the cementation of deposited sediment such as sand, silt, gravels ect. from pre existing rocks .
Continues deposition of weathered rocks by agent of denudation such as water, wind and glaciation at a particular
place in chronological manner(sorting) process of large particles, followed by medium size particle, small size
particles and finally fine coarse debris.
• The overlying rocks compress the underlying rocks to reduce the pores spacing leading to cementation and less
compaction. The sorting process of debris three types of mechanically formed sedimentary rocks. And they are
tabulated below
TYPES OF MECHANICALLY FORMED
SEDIMENTARY ROCKS
MODE OF FORMATION EXAMPLES
RUDACEOUS This is formed from the litification of large
fragment of rocks carried by agents of
erosion. The size of the grains are above
2mm
Breccia and conglomerate
ARENACEOUS This is formed from the litification of
medium size sediments of rocks of
about 0.062 – 2mm
Sandstone and gritstone
AGRILLACEOUS This is formed from the litification of
small or fine particles of about
1/16mm in diameter.
Clay, mudstone and shale
OCCLUDED PFOF. 13

14. ORGANICALLY FORMED SEDIMENTARY ROCKS
They are formed from the accumulation and litification of remains of dead living organisms such as plant and animals. They contain
fossils and they included calcareous rocks, carbonaceous rocks and Siliceous rocks.
CALCAREOUS ROCKS: formed from shells and skeleton of dead animals .examples. Limestone and chalk
CARBONACEOUS ROCKS: formed from dead vegetation, carbon constitute. Examples. Lignite, anthracite, peat and coal
SILICEOUS ROCKS: formed from remains or decay of aquatic plants and animals such as sponges and radiolarians.
Nb. Crude oil are mainly derived from organically formed sedimentary rocks
chCHEMICALLY FORMED SEDIMENTARY ROCKS
from evaporation or precipitation of chemicals in solutions. Solution rock particles are made dry after evaporation. The main forms of
ch
These are derived chemically formed sedimentary rocks are
CARBONATES: Formed from the precipitation of carbonate in solutions. Including dolomite and travertine
SULPHATE: formed from the precipitation and desiccation of sulphate in solutions. Including gypsum and anhydrite
CHLORIDE: formed from the evaporation and desiccation of sodium chloride(NaCl) from a highly saline water body such as the sea.
Including common salt or salt crystals.
METAMORPHIC ROCKS
The word metamorphic came from the word “metamorphism” which is a Greek word. According to the Greeks, Metamorphism was a
combination of the word “Meta” meaning change and “Morph” meaning form. So metamorphism means to change form.
Metamorphic rocks are formed from the deformation and foliation of existing rocks by the activities of heat, pressure and active fluids.
These changes can be the size, shape, texture and the mineral constituent of pre existing rock (either sedimentary or igneous). Rocks
that form when a pre-existing rock (protolith) changes due to temperature or pressure, and/or as a result of squashing or shearing.
Protolith – the pre-existing rock.
Metamorphism doesn’t include weathering, diagenesis, and melting
OCCLUDED PFOF. 14

15. CHARACTEERISTICS OF METAMORPHIC ROCKS
I. They are hard and resistant
II. More cemented and compact than pre – existing rocks
III. Non – fossilized
 MODE OF FORMATION
when pre – existing rocks are subjected to intense
heat, high pressure or both, the original rock is likely to
change physically or chemically, it composition, character
or appearance. It is formed as a result of heat that
accompanis mountain building movement of the earth
crust.
if the mineral structure demonstrates a particular
alignment after metamorphism, the rock is called foliated.
Moreover, some minerals may appear in wavy striations.
Examples are gneiss, slate and schist.
however, parent rocks with more homogeneous
(evenly mixed) constituent may produce non – foliated
rocks. Examples of non – foliated rocks are marble,
quartize etc.
These form the two main types of metamorphic
rocks OCCLUDED PFOF. 15

16. FOLIATED METAMORPHIC ROCKS :
WHEN THE MINERAL STRUCTURE
DEMONSTRATES A PARTICULAR
ALIGNMENT OR A WAVY
STRIATIONS
SCHIST
GNEISSMIGMATITE
MINERAL
STRUCTURE
CHANGE FROM
SHALE
INTENSE HEATING AND
COMBINATION OF
PARTIALLY MELTED
METAMORPHIC ROCKS
FROM GNEISS
A WAVY
STRIATION
FROM
GRANITE
OCCLUDED PFOF. 16

17. OCCLUDED PFOF. 17

18. Metamorphic rocks that have recrystallized and/or neocrystallized but do not typically have a foliation (usually
because grains are not sufficiently elongated). Distinguished based on composition, but may be foliated if
subjected to significant differential stress
AMPHIBOLITE: A
RECRYSTALIZATION OF
BASALT OR GABRRO
QUARTIZE: AN INTERLOGING PORE
SPACING COMPACTED OR
ELIMINATED FROM QURTZ
SANDSTONE
SHALE
SLATE
OCCLUDED PFOF. 18

19. • PARENT ROCKS
• Sandstone  Quartzite
• Limestone  Marble
• Shale  Slate
• Granite  Gneiss
• Clay  Slate
• Coal  Graphite
• Gabbro  Schist
• Shale  Schist
Below are some economic importance of rocks.
1. Source of water: some rocks are sources of water for some rivers and
man gets water from percolating water that is retain by permeable
rocks called aquifer.
2. Source of soil: some rocks serve as sources of soil most especially
when rocks disintegrate or weather. The fine deposited particles of
rocks form soils. Which are used for faming activities. For example,
Basalt weather relatively quickly into a deep fertile soil. South eastern
Brazil is large coffee growing area because the place sits on the
Deccan Plateau, a composite of Basalt.
3. Source of food: Rock salt serve as an important source of food. This is
a chemically derived sedimentary rock. Example is Daboya in the
northern region of Ghana, where the soil has salt constitute.
4. Industrial raw materials: some of the rocks serve as raw materials for
feeding industries. Limestone serve as raw materials to cement
factories.
5. Source of minerals. Examples gold, diamond, manganese etc.
6. Source of employment: people are employed in the extraction of
minerals from rocks. Quarry is an important source of employment to
the developing countries. Mining activities leads to the employment
of both skilled and non skilled labour.
7. Source of tourists attraction 8. source of revenue to the government
OCCLUDED PFOF. 19

20. OCCLUDED PFOF. 20

21. The study of rocks actually attest to deformation and
reformation of rocks which leads to ceaseless process of
cycle of rock formation.
• ROCK CYCLE: It refers to the interrelationships among
the three rock groups or types and the processes that
create or act to transform one rock type to another.
• The rock cycle begins with the development of magma
in the earth’s crust. As molten rocks eventually cools,
solidify and crystalize, igneous rocks are formed.
• When these igneous rocks come into contact with the
atmosphere, the slowly disintegrate and decomposed
through weathering.
• The weathered particles are lithified to form
sedimentary rocks after deposition.
• Also, if buried sedimentary rocks are subjected to great
heat and pressure they are transformed to form
metamorphic rocks.
• It is important to note that some changes directly to the
other, for example some igneous rocks may turn directly
to metamorphic rocks after exposure to intense heat
and pressure
SUMMARY
OCCLUDED PFOF. 21

22. OCCLUDED PFOF. 22