Transcript igneous rocks

Understanding Geology and Its
Engineering Properties…
From A Civil Engineer’s Point of View…
Dr.ÖZGÜR YILMAZER
Geotechnical Engineer
MSc. Geological Engineering
MSc. Civil Engineering
PhD. Geological Engineering
INTRODUCTION
ROCKS (Definition: Minerals)
A rock is defined as a consolidated mixture of minerals. A mixture of
minerals implies the presence of more than one mineral grain, but not
necessarily more than one type of mineral. A rock can be composed of
only one type of mineral, but most rocks are composed of several
different types of minerals.
A mineral is;
•a naturally occurring substance
•that is solid and stable at room temperature,
•representable by a chemical formula,
•usually abiogenic, and
•has an ordered atomic structure.
It is different from a rock, in this sense, which can be an aggregate of
minerals or non-minerals, and does not have a specific chemical
composition.
INTRODUCTION
ROCKS (Definition: Minerals)
There are over 4,900 known mineral species. The silicate minerals
compose over 90% of the Earth’s crust. Silicon and oxygen constitute
approximately 75% of the Earth's crust, which translates directly into the
predominance of silicate minerals.
INTRODUCTION
ROCKS (Definition: Minerals)
Minerals are distinguished by various chemical and physical
properties. Differences in chemical compositon and crystal structure
distinguish various species, and these properties in turn are influenced
by the mineral's geological environment of formation.
Minerals are made of elements that are bonded together to form
stable solid matters. Hydrogen and Oxigen elements bond together to
form H2O (water) mineral. Similarly, Na and Cl elements come together
to form NaCl (salt).
INTRODUCTION
ROCKS (Definition: Elements)
A chemical element is a pure chemical substance consisting of one
type of atom distinguished by its atomic number, the number of protons
in its nucleus.
INTRODUCTION
ROCKS (Definition: Elements)
When two distinct elements are chemically
combined, with the atoms held together by
chemical bonds, the result is termed a
chemical compound.
Q_1. How do atoms bond together to form
minerals?
A_1. Elements bond by sharing or transferring
electrons
Q_2. Why don't elements prefer to remain
alone, unbonded?
A_2. Elements like to have their outer electron
orbital full of electrons, so elements with full
orbitals are very stable (e.g., the noble gases
He, Ar, Kr, Xe).
ROCK TYPES
Rocks are grouped into three main categories:
ROCK CYCLE
IGNEOUS ROCKS
DEFINITION AND SOURCES
Igneous rocks (from the Greek word for fire) form from molten rock (magma),
crystallizes and solidifies. Igneous rocks form in three main places: where
lithospheric plates pull apart at mid-ocean ridges, where plates come together at
subduction zones and where continental crust is pushed together, making it thicker
and allowing it to heat to melting.
INTRODUCTION
ROCKS
Igneous rocks are divided into two groups, intrusive and extrusive,
depending upon where the molten rock solidifies
IGNEOUS ROCKS
DEFINITION : INTRUSIVE ROCKS
Intrusive, or plutonic
igneous rock forms
when
magma
is
trapped deep inside
the
Earth.
Great
globs of molten rock
rise
toward
the
surface. Some of the
magma may feed
volcanoes on the
Earth's surface, but
most remains trapped
below, where it cools
very
slowly
over
many thousands or
millions of years until
it solidifies.
IGNEOUS ROCKS
DEFINITION : INTRUSIVE ROCKS
Slow cooling means the
individual mineral grains have
a very long time to grow, so
they grow to a relatively large
size. Intrusive rocks have a
coarse grained texture. The
image at right shows granite,
an intrusive igneous rock..
IGNEOUS ROCKS
DEFINITION : EXTRUSIVE ROCKS
Extrusive, or
volcanic,
igneous rock is
produced when
magma exits
and cools
outside of, or
very near the
Earth's surface.
IGNEOUS ROCKS
DEFINITION : VOLCANIC (EXTRUSIVE) ROCKS
These are the rocks that
form at erupting
volcanoes. The magma,
called lava when molten
rock erupts on the
surface, cools and
solidifies almost instantly
when it is exposed to the
relatively cool temperature
of the atmosphere.
IGNEOUS ROCKS
DEFINITION : EXTRUSIVE ROCKS
Quick cooling means that
mineral crystals don't have
much time to grow, so
these rocks have a very
fine-grained or even glassy
texture. Hot gas bubbles
are often trapped in the
quenched lava, forming a
bubbly, vesicular texture.
Pumice, obsidian, and
basalt are all extrusive
igneous rocks.
IGNEOUS ROCKS
DEFINITION : ROCK TEXTURE
Igneous rock textures are used by geologists in determining the mode of origin
igneous rocks and are used in rock classification. There are six main types of textures;
1) Phaneritic,
2) Aphanitic,
3) Porphyritic,
4) Glassy,
5) Pyroclastic and
6) Pegmatitic.
Aphanitic (not visible) rocks in contrast to Phaneritic rocks, typically form from lava
which crystallize rapidly on or near the Earth‘s surface. Because they make contact with
the atmosphere they cool quickly, so the minerals do not have time to form large
crystals. The individual crystals in an aphanitic igneous rock are not distinguisable to the
naked eye. Examples of aphanitic igneous rock include basalt, andesite, and rhyolite.
IGNEOUS ROCKS
DEFINITION : ROCK TEXTURE
Glassy or vitreous textures occur during some volcanic eruptions when the lava is
quenched so rapidly that crystallization cannot occur. The result is a natural
amorphous glass with few or no crystals. Examples include obsidian and pumice.
Phaneritic (phaner = visible) textures are typical of intrusive igneous rocks, these
rocks crystallized slowly below the Earth's surface. As a magma cools slowly the
minerals have time to grow and form large crystals. The minerals in a phaneritic
igneous rock are sufficiently large to see each individual cyrstal with the naked eye.
Examples of phaneritic igneous rocks are gabro, diorite and granite.
Pegmatitic texture occurs during magma cooling when some minerals may grow so
large that they become massive (the size ranges from a few cm to several metres).
IGNEOUS ROCKS
DEFINITION : ROCK TEXTURE
Porphyritic textures develop when conditions during cooling of a magma change
relatively quickly. The earlier formed minerals will have formed slowly and remain as
large crystals, whereas, sudden cooling causes the rapid crystallization of the
remainder of the melt into a fine grained (aphanitic) matrix. The result is an aphanitic
rock with some larger crystals (phenocrysts) imbedded within its matrix. Porphyritic
texture also occurs when magma crystallizes below a volcano but is erupted before
completing crystallization thus forcing the remaining lava to crystallize more rapidly
with much smaller crystals.
IGNEOUS ROCKS
DEFINITION : ROCK TEXTURE
Pyroclastic (pyro=igneous, clastic = fragment) textures occur when explosive
eruptions blast the lava into the air resulting in fragmental, typically glassy material
which fall as volcanic ash, lapilli, and volcanic bombs.
SUMMARY
IGNEOUS ROCKS
SUMMARY
IGNEOUS ROCKS
SUMMARY
IGNEOUS ROCKS
Intrusive igneous
rocks are the rocks
which cool down
really slowly under
the surface. All
igneous rocks
doesn’t cool the
same way. That’s
the reason why they
don’t look all the
same too. Intrusive
igneous rocks have
large crystals. The
granite stone is the
example of intrusive
igneous rock.
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