geology

1. RocksRocks
Rocks are divided by origin into three types:
1. Igneous Rocks: are formed from the solidification of
molten rock material. whether crystallized on the surface and
below the surface or in the ground.
Arock is a naturally formed, consolidated material usually
composed of grains of one or more minerals.
Petrology: Which is interested in studying rocks, origin,
composition and physical properties and the nature of the
changes taking place due to the different geological
processes.
rocks and minerals Considered of the main components of the
earth's crust.
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2. 2. Sedimentary Rocks: are the secondary
rocks which are formed from the loose
fragments or clastic sediments produced
by weathering of older rocks.
3.Metamorphic Rocks: which are
formed from other rocks by
Metamorphism process due to the effects
of High temperature, High pressure and
Chemical fluids
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3. Rock Cycle in nature
The rock cycle shows how one type of rocky material gets
transformed into another
• Magma is created by melting of rock above a subduction
zone
• Less dense magma rises and cools to form igneous rock
• Igneous rock exposed at surface gets weathered into
sediment
• Sediments transported to low areas, buried and pressured
into sedimentary rock
• Sedimentary rock heated and pressured at depth to form
metamorphic rock
• Metamorphic rock may heat up and melt at depth to form
magma 3

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5. • Igneous rocks are formed from two basic types:
Formation of Igneous Rocks
Intrusive or Plutonic rocks: Intrusive rocks form when
magma solidifies underground and the slow cooling to form
large crystals, it is known as gragunal texture. Examples of
intrusive igneous rocks are granite , diorite, gabbro, and
peridotite.
Extrusive or Volcanic rocks: Extrusive rocks form when
magma solidifies at the Earth’s surface (lava) where they
cool quickly to form small crystals, it is known as Aphanitic
texture. These rocks include rhyolite , andesite, basalt
, dacite. Some cool so quickly that they form glass texture
such as obsidian, pumice
1- Igneous Rocks1- Igneous Rocks
• Magma is molten rock.
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6. • Intrusive rocks exist in bodies or structures that penetrate
or cut through pre-existing country rock
• Intrusive or Plutonic bodies are given names based on
their size, shape, depth and relationship to country rock
– Shallow intrusions: Dikes and sills
FORMS OF INTRUSIVE IGNEOUS ROCKS
Dikes: Dikes are relatively thick tabular sheetlike body that
penetrates virtically to the bedding planes.
Mafic
dyke
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7. SILLS: Sills are relatively thin tabular
sheetlike body that penetrates parallel to
the bedding planes.
• They are discordant
• Cut across the bedding of the rocks in which they
intrude
• Thickness vary widely from an inch upto hundred
of feet
• Injected through fractures, joints, and weak planes
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8. Depth intrusions: Laccolith, Phacolith, Lopolith, Batholith
Laccolith: It is a concordant
body, with flat bottom and
convex upward. It is dome
shaped
Phacolith: These are
concordant bodies that
occurs along the crests and
troughs of the folded
sedimentary strata.
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9. Batholith: are the largest
kind of plutons, irregular
in shape and occupies
large area.
Stocks: Are smaller irregular
bodies with 10 km in
maximum dimension, and are
associated with batholiths.
Lopolith: These are basin
or saucer-shaped concordant
bodies with top nearly flat
and convex bottom.
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Extrusive rocks:
volcanic rocks are in the form of large lamellar
bodies produced from the flow of magma on
the earth surface and be irregular in shape and
called by lava: may be
1. scoria: the upper surface of the lava filled by
the gaps as a result of the escape of gases.
2.Ropy: Contains long protrusions and curved-
like mountains.
3. Blocky: The blocks are irregularly shaped

11. Classification of Igneous RocksClassification of Igneous Rocks
1- Mode of formation: Volcanic and PlutonicVolcanic and Plutonic
2- Texture of rocks: Textural classified into:
– Plutonic rocks (gabbro-diorite-granite) are coarse-
grained and cooled slowly at depth
– Volcanic rocks (basalt-andesite-rhyolite) are
typically fine-grained and cooled rapidly at the
Earth’s surface
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12. 3- Mineralogical Composition: are divided into:
1. Major minerals include sillicate minerals:
- Acidic rocks composed of silica and aluminum bearing
minerals and light-colored (e.g. quartz, orthoclace,
plagioclace and muscovite ).
-Basic rocks composed of magnesium and iron bearing
minerals and dark-colored (e.g. biotite, pyroxene, hornblend
and olivine).
2. Secondary minerals:
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13. • 4- Chemical Composition: particularly silica (SiO2)
content, determines mineral content and general color
of igneous rocks
– Felsic (silicic) rocks have >65% silica, by weight,
and contain light-colored minerals that are abundant
in silica, aluminum, sodium and potassium
• Intrusive/extrusive felsic rocks - granite/rhyolite
– Intermediate rocks have 65-52% silica, by weight
• Intrusive/extrusive intermediate rocks -
diorite/andesite
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14. – Mafic rocks have 52-40% silica, by weight, and
contain dark-colored minerals that are abundant
in iron, magnesium and calcium
• Intrusive/extrusive mafic rocks- gabbro/basalt
– Ultramafic rocks have <40% silica, by weight,
and are composed almost entirely of dark-
colored ferromagnesian minerals
• Most common ultramafic rock is peridotite
(intrusive)
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16. Granite is a coarse-grained,
light colored, intrusive
igneous rock that contains
mainly quartz, feldspar, and
mica minerals.
Rhyolite is a light-colored,
fine-grained, extrusive igneous
rock that typically contains
quartz and feldspar minerals.
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17. Diorite is a coarse-grained,
intrusive igneous rock that
contains a mixture of feldspar,
pyroxene, hornblende and
sometimes quartz.
Andesite is a fine-
grained, extrusive igneous
rock composed mainly
of plagioclase (anorthite),
hornblende and biotite.
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18. Basalt is a fine-grained, dark-
colored extrusive igneous rock
composed mainly
of plagioclase and pyroxene.
Gabbro is a coarse-grained,
dark colored, intrusive
igneous rock that contains
feldspar, pyroxene and
sometimes olivine.
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19. Peridotite is a coarse-grained intrusive igneous rock
that is composed almost entirely of olivine. It may
contain small amounts of amphibole, feldspar, quartz or
pyroxene.
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