MODULE 3 – ROCKS
I.LEARNING OUTCOMES:
1.) Determine how rocks are formed and how are they classified
2.) Identify rock samples based on their characteristics and be familiar of their economic
values and where they are located in our country
3.) Integrate simple ways of conserving rocks by patronizing products made of materials
that can easily be replaced in nature to discourage illegal mining of decorative stones
and quarrying which hastens soil erosion
II. CONCEPTS:
A. ROCKS CYCLE:
Rock is any solid mass of mineral or mineral-like that occurs naturally as part of our
planet. The Earth is a system. This means that our planet consists of many interacting parts
that form a complex whole. The rock cycle allows us to view many of the interrelationships
among different parts of the Earth system. It helps us understand the origin of igneous,
sedimentary and metamorphic rocks and to see that each type is linked to the others by the
process that act upon and within the planet.
B. TYPES OF ROCKS:
1. IGNEUOS ROCKS
Igneous rocks form as molten rocks cool and solidify. Its parent material is magma which is
formed by partial melting that occurs at various levels within the Earth’s crust and upper
mantle at depths that may exceed 200 kilometers.
TYPES OF IGNEOUS ROCKS
Extrusive Igneous Rocks – igneous rocks that form when molten rocks solidify
at the surface.
Intrusive Igneous Rocks – also called plutonic rocks and form at depth when
magma loses its mobility before reaching the surface.
CRYSTALLIZATION OF MAGMA
In the process of crystallization, cooling reverses the events of melting. As the
temperature of the liquid drops, the ions pack closer together and begin to lose their freedom
of movement. When cooled sufficiently, the forces of the chemical bonds will again confine the
atoms to an orderly crystalline arrangement. The earliest formed minerals have space to grow
and to have better developed crystal faces than do the latter ones that fill the remaining space.
Eventually, all of the magma is transformed into a solid mass of interlocking silicate
minerals called igneous rocks.
TYPES OF IGNEOUS TEXTURES
Texture describes the over-all appearance of the rock based on size, shape and
arrangement of its interlocking crystals, this reveals a great deal about the environment in
which the rock formed.
APHANITIC Texture (fine-grained texture)
The crystals are too small for individual minerals to be distinguished with
the unaided eye. Igneous rocks that form at the surface or as small masses
within the upper crust where cooling is relatively rapid possess very fine-
grained texture.
Light, intermediate or dark in color, has spherical or elongated openings
called vesicles left by gas bubbles that escape as magma solidifies that are
most abundant in the upper portion of lava flows where cooling occurs very
rapidly.
PHANERITIC Texture ( coarse-grained)
Coarse-grained igneous rocks are formed when large masses of magma
solidify slowly below the surface. Consists of a mass of intergrown crystals
which are roughly equal in size and large enough that the individual crystals
can be identified with the unaided eye.
PORPHYRITIC Texture
Different minerals crystallize at different temperatures and at different
rates, it is possible for some crystals to become quite large before others
begin to from. If magma containing large crystals should change environment
like erupting at the surface, the molten portion of the lava would cool quickly
resulting in rocks which has large crystals embedded in a matrix of smaller
crystals.The large crystals are called phenocrysts and the matrix of smaller
crystals is called groundmass.
GLASSY Texture
During a volcanic eruption, molten rock is ejected into the atmosphere
where it is quenched quickly. Rapid cooling may generate rocks with glassy
texture.
CLASSIFICATION OF IGNEOUS ROCKS
https://tiu.edu.iq/engineering/civil/wp-content/uploads/2019/02/Lec.-GEO-3.pdf
2. SEDIMENTARY ROCKS
Rock formed from weathered products of pre-existing rocks that have been
transported, deposited and lithified. Sediments are deposited at the Earth’s surface so the rock
layers that eventually form contain within them indications of past environments in which their
particles were deposited and clues to the mechanisms involved in their transport. Contain
fossils which are vital tools in the study of the past.
TYPES OF SEDIMENTARY ROCKS
A. CLASTIC OR DETRITAL – rocks that are composed of fragments of older rocks.
EXAMPLES:
SHALE – consists of silt and clay-sized particles, fine-grained and the tiny
grains indicate that deposition occurs as the result of gradual settling from
relatively quiet, nonturbulent currents.
Economic Values: used as raw material for the production of pottery, bricks,
tiles and china wares, making of cement and can be a source
of energy.
SANDSTONE – rocks in which sand-sized grains predominate and quartz is the
predominant mineral in most sandstones.
Economic Value: quartz is the primary ingredient of glass
CONGLOMERATE – consists largely of gravel-sized particles and the particles
are large enough to be identified as distinctive rock types.
Economic Values: used in construction, roads and as dimension stone for
decoration of walls and floors
BRECCIA – if the size of the large particles are angular rather than rounded.
Economic Value: used in sculptural and architectural designs like statues, walls
and columns
https://slideplayer.com/slide/4196068/
B. CHEMICAL SEDIMENTARY ROCKS - consists of a material that is precipitated from water
either inorganic or organic means.
EXAMPLES:
LIMESTONE – considered as the most abundant and is composed of
the mineral calcite. The mineral composition of all
limestone is similar but different types exist because
they are produced under a variety of conditions.
Coral reefs - corals are capable of creating large quantities of
marine limestone.
Coquina – a biochemical limestone which is a coarse rock
composed of poorly cemented shell fragments.
Chalk – a soft, porous rock made up almost entirely of the hard
parts of microscopic marine organisms.
Travertine – having an inorganic origin that forms when
chemical changes or high water temperatures increase
the concentration of calcium carbonate. These are
commonly found in caves with groundwater as the
source of calcium carbonate.
DOLOSTONE – composed of calcium-magnesium carbonate mineral
called dolomite. Most originate when magnesium in sea
water replaces some of the calcium in limestone.
CHERT – the name used for a number of very compact and hard rocks
made of microcrystalline silica.
Flint – the dark color results from the organic matter that it
contains.
Jasper – has red color which is from iron oxide.
Agate – has a banded form
EVAPORITES
Halite (sodium chloride or salt) – used for cooking, melting of
ice on roads and making hydrochloric acid.
Gypsum – the basic ingredient of plaster of Paris which is used
extensively in the construction industry for
wallboard and interior plaster.
COAL – made mostly of organic matter or remains of past life forms
buried deeply for a long period of time.
https://slideplayer.com/slide/4196068/
SEDIMENTARY ROCKS REPRESENT PAST ENVIRONMENTS
Sedimentary rocks are important in interpretation of Earth’s history because
understanding the conditions under which sedimentary rocks form, geologists can deduce the
history of a rock, including information about the origin of its component particles, the method
and length of sediment transport and the nature of the place where the grains eventually came
to rest. Thus when a series of sedimentary layers are studied, the successive changes in
environmental conditions that occurred at a particular place with the passage of time can be
seen.
Sediments are deposited at the Earth’s surface, thus, they hold many clues about
the physical, chemical and biological conditions that existed in the areas where the materials
accumulated. Other features found in some sedimentary rocks are ripple marks, mud cracks
and fossils also give clues to past environments.
ENERGY SOURCES FROM SEDIMENTARY ROCKS
A. COAL
Commonly called a fossil fuel and has been an important fuel for
centuries. In the 19th century and early 20th century, cheap and plentiful coal powered
the industrial revolution. Coal remains the major fuel used in power plants to generate
electricity. As oil reserves gradually diminish in the years to come, the use of coal may
increase.
Air pollution is a major problem associated with the burning of coal. It also
includes the formation of acid rain from the sulphur which coal contains.
B. PETROLEUM AND NATURAL GAS
Oil and natural gas commonly occur together in the pore spaces of
sedimentary rocks, consists of hydrocarbon compounds mixed together. Petroleum
formation is associated with the accumulation of sediment in an ocean areas that are
rich in plant and animal remains that become buried and isolated in an oxygen-deficient
environment. As the mobile petroleum and natural gas form, they migrate and
accumulate in adjacent permeable beds such as sandstone.
3. METAMORPHIC ROCKS
A. Metamorphism – transformation of one rock type into another due to heat, pressure
and chemically active fluids.
B. Settings Where Metamorphism Mostly Occurs:
1. When a rock is near or touching a mass of magma. Here the changes are caused by
the high temperatures of molten material that “bakes” the surrounding rock
2. The least common type occurs along fault zones and is called cataclastic
metamorphism, here rock is broken and pulverized as crustal blocks on
opposite sides of a fault grind past one another.
3. During mountain building, great quantities of rock are subjected to differential
forces and high temperatures associated with large scale deformation and the end
result may be extensive areas of metamorphic rocks.
C. Agents of Metamorphism:
1. Heat – provides the energy to drive chemical reactions that result in recrystallization
of minerals. Rocks formed near the Earth’s surface may be subjected to intense
heat when intruded with molten material rising from below. At convergent
boundaries, rocks are slowly thrust downward to become metamorphosed at
depth.
2. Pressure and Stress - buried rocks are subjected to stress or force exerted by the load
above. Rocks are also subjected to directional tectonic forces during mountain
building, these forces, which are unequal in different directions are called
differential stresses
3. Chemical Activities/Chemically active fluids - the common fluid is water-containing
ions in solution, some water is contained in the pore spaces of every rock.
Water aids in chemical reactions, also surrounds crystals and act as a catalyst by
aiding ion migration. In some instances, water promotes the recrystallization of
minerals.
D. How Metamorphism Alters Rocks - metamorphic processes cause many changes in rocks
like;
1. Increased density
2. Growth of larger crystals
3. Reorientation of mineral grains
4. Transformation from low temperature to high temperature minerals
E. TYPES OF METAMORPHISM
1. Contact Metamorphism - this occurs when magma invades a cooler rock, a zone of
alteration called an aureole that forms around the emplaced magma. Near the
magma body, high temperature minerals like garnet may form and farther
away, low grade minerals like chlorite is produced. Most contact metamorphic
rocks are fine-grained, dense, rough and of various chemical compositions.
2. Regional Metamorphism - occurs where rocks are squeezed between two converging
plates during mountain building. During mountain building, large segments of
the earth’s crust are intensely squeezed and become highly deformed. As the
rocks are folded and faulted, the crust is shortened and thickened. This
general thickening results in terrains that are lifted high above sea level.
F. Types of Metamorphic Rocks
1. Foliated Metamorphic Rocks
Slate - fine-grained foliated, composed of mica flakes
has excellent rock cleavage or tendency to break into flat slabs
generated from low-grade metamorphism of shale
used in roofing, floor tiles, blackboards and billiard tables
its color depends on mineral constituents
Black – (carbonaceous) contains organic material
Red – gets its color from iron oxide
Green – contains chlorite
Phyllite – can easily be distinguished from slate by its glossy sheen
exhibits rock cleavage
composed of very fine crystal of either muscovite or chlorite
Schist – strongly foliated rocks that can be readily split into thin flakes or slabs
contain more than 50% platy and elongated minerals that commonly
include mica (muscovite, biotite) and amphibole
formed from more intense metamorphism, most from major
mountain building processes
Gneiss – banded metamorphic rocks that contain mostly elongated and
granular minerals
common minerals are: quartz, potassium, feldspar and sodium
feldspar, lesser amounts of muscovite, biotite and hornblend
most break in irregular fashion
2. Non-foliated Metamorphic Rocks
Marble – a coarse, crystalline rock with limestone or dolostone as parent
material
pure marble is white and composed of the mineral calcite
colors of marble are caused by impurities, it can be pink, gray, green
or black
under extreme deformation, banded marble appears to have an
artistic design and used as building stones and carvings for statues
and monuments
Quartzite – very hard metamorphic rock formed from quartz sandstone
typically white but iron oxides can produce reddish or pinkish
color
https://slideplayer.com/slide/4196068/
III. REFERENCES:
A. BOOKS
Thompson and Turk, Introduction to Earth Science, 2012
Braganza, C. S., Earth Science, 2005
Tarbuck and Lutgens, Earth Science, 2002
Timothy Kusky, Ph.D. ENCYCLOPEDIA OF Earth and Space Science, 2010
Thompson and Sammonds, Advances in Earth Science From Earthquakes to Global
Warming, 2007
B. INTERNET SOURCES
https://tiu.edu.iq/engineering/civil/wp-content/uploads/2019/02/Lec.-GEO-3.pdf
https://slideplayer.com/slide/4196068/
https://slideplayer.com/slide/4196068/
https://www.exploringnature.org/db/view/Rock-Identification-and-the-Rock-Cycle
