Igneous Rocks
Chapter 5
Vocabulary
• Radioactivity-the spontaneous
process through which
unstable nuclei emit radiation.
• Lava-magma that flows out
onto Earth’s surface.
• Igneous rock- rocks formed
from the crystallization of
magma.
Vocabulary
• Partial melting- the process by
which some minerals melt at low
temperatures while other remain
solids.
• Fraction crystallization- the process
by which different minerals from
at different temperatures.
• Bowen’s Reaction Series- a model
that describes the relationship
between cooling magma and
mineral formation.
Composition and Origins of Magma
I. Composition of magma
A. Magma is a mixture of molten rock, gases, and
mineral crystals.
B. The elements in magma are the eight major elements
in Earth’s crust.
1. The most abundant compound in magma
is Silica (SiO2).
C. Magmas are classifies as basaltic, andesitic, and
rhyolitic.
1. Their classification depends on how much
silica they contain.
Composition and Origins of Magma
Temperature
Increase with depth
In Earth’s crust.
This is known as the
geothermal gradient.
Water content
As this increases, the
melting point
decreases.
Pressure
Factors in the
formation of
magma
Increases with depth
under the surface
Which increases the
melting point of rock
Mineral content
Different minerals
have different
melting points.
How Rocks Melt
When a rock begins to melt, the minerals with
the lowest melting point melt first. The elements
in these minerals from the liquid part of magma.
As other minerals melt, the elements in those
minerals are added to the magma and change its
composition. The opposite happens as the
magma cools. The elements in the minerals are
removed from the magma in the order that the
minerals crystallize, which is fractional
crystallization.
Bowen’s Reaction Series
Partial Melting
Partial melting is when
different minerals within a
rock melt at different rates.
When different minerals are
melted new elements are
added to the magma
mixture changing the
chemical composition.
Synthesize
Both branches show that minerals from
in predictable patterns in cooling
magma. However, in the right branch,
the feldspar minerals undergo
continuous change. The ironmagnesium minerals, in the left branch,
undergo abrupt changes.
Section 5.2 Vocabulary
Magma- molten material found under
Earth’s surface.
Intrusive Rock- Igneous Rock that cool slowly
beneath Earth’s surface.
Extrusive Rock- Igneous rock that cool quickly
on Earth’s surface.
Granitic Rock- Light-colored rock high in silica
and contains quartz and feldspar.
Basaltic Rock- Dark-colored rock low in silica
and contains iron and magnesium-rich
materials.
Section 5.2 Vocabulary Cont.
Texture- the size, shape, and distribution of crystals
or grains that make up a rock.
Porphyritic texture- characterized by large, wellformed crystals surrounded by finer-grained crystals
of the same mineral or different minerals.
Vesicular Texture- A spongy appearance caused by
broken gas bubbles
Pegmatite- veins of extremely large grained
minerals.
Kimberlite- a rare, ultramafic variety of peridotite
that forms pipe like structures and which sometimes
contain diamonds.
Types of Igneous Rock
Intrusive
Extrusive
Igneous
Rocks
- Fine-grained
-Cool slowly Formed by - Cool quickly
crystallizat
-Form
- Form above
ion
of
beneath
surface
magma
surface
- Ex. Rhyolite
Ex. granite
-Coarsegrained
Mineral Composition
1. basalt: ___________________________
A fine-grained rock containing
_______________________________
plagioclase, feldspar, biotite, pyroxene,
_______________________________
amphibole, and olivine
A felsic extrusive, noncrystalline rock
2. obsidian: ______________________________
rock that contians only
3. peridotite: A_________________________
pyroxene and olivine
__________________________
coarse-grained rock that is mostly
4. diorite:A____________________________
white,
gray, and black
____________________________
5. pegmatite: a_________________________
very coarse-grained rock that
__________________________
contains potassium feldspar
Grain Size
Describe the conditions that cause igneous rocks
to form large grains or no visible grains.
Intrusive igneous rocks are formed when
magma cools slowly beneath Earth’s surface,
so large crystals have time to form. Extrusive
igneous rocks cool quickly because they are
exposed to air and moisture on Earth’s
surface, so visible crystals do not have time to
form.
Igneous Rocks as resources
List two characteristics of igneous rocks that
make them good building materials.
1. They have interlocking grain textures,
which give them strength.
2. They contain minerals that are
resistant to wearing.
Ore Deposits
The fluid from which
Magma crystallizes
Contains high levels
Silica, water, and
of ______________
Leftover elements
________________.
The fluid fills
___________
Cracks, and
___________
Voids in the
________.
rock
The fluid solidifies to form
Quartz veins containing
____________
gold
Metals such as _____,
silver ____,
lead _______,
copper and
_______,
Rare elements such as
________
lithium and __________.
beryllium
Answer the synthesize question.
Other Information
Igneous is Latin for “from fire”