Transcript Guided Notes for Igneous Rocks

Guided Notes for Igneous
Rocks
Chapter 5, Section 1
1) How are igneous rocks formed?
 Igneous
rocks are formed from
the crystallization of magma as it
cools.
2) What is lava?
 Lava
is magma that flows out
onto Earth’s surface.
3) What are extrusive igneous
rocks?
 Extrusive
rocks are fine-grained
igneous rocks that cool quickly on
the Earth’s surface.
4) What are intrusive igneous
rocks?
 Intrusive
rocks are coarse-grained
igneous rocks that cool slowly
beneath the Earth’s surface.
5) What is magma?..


Magma is a slushy mixture of molten
rock, gases, and mineral crystals.
Elements found in magma include
oxygen, silicon, aluminum, and iron
6) Why is silica an important
magma compound?
 Because
silica is the most
abundant compound in magma, it
has the greatest effect on magma
characteristics.
7) What are the 3 classes of
igneous magma, and how…


The 3 classes of magma are basaltic,
andesitic, and rhyolitic.
They are classified according to their
silica content.
8) At what temperatures do rocks
melt?...


Rocks melt at temperatures between
800°C and 1200°C.
These temperatures are found in the
upper mantle and lower crust.
9) State the four factors that affect
magma formation…
(a)
(b)
(c)
(d)
temperature—increases with depth in the
Earth’s crust
Pressure—as pressure on a rock increases, its
melting point also increases
Water content—as water content increases,
melting point decreases
Mineral composition—oceanic crust is rich in
iron and magnesium and melts at higher
temperatures than continental crust, which is
rich in aluminum and silicon
10) Explain why magma is often a
slushy mix of crystals…

Because different minerals have
different melting points, not all parts
of a rock melt at the same time.
Thus, this partial melting is why
magma is slushy.
11) What is fractional
crystallization…

When magma cools, it crystallizes in
the reverse order of partial melting.
Fractional crystallization is the
process by which the first minerals to
crystallize from magma are the last to
melt during partial melting.
12) Name 4 properties by which
geologists classify igneous rocks.
 Intrusive
or Extrusive
 Mineral Content
 Grain Size
 Texture
13) Describe the mineral
composition of the 3 major groups..



Felsic—high silica content, contain quartz
and feldspar crystals (ex. Granite)
Mafic—low silica content, rich in iron and
magnesium (ex. Gabbro)
Intermediate—moderate amount of silica,
contains biotite, amphibole, pyroxene (ex.
Diorite)
14) Why do some igneous rocks
have large mineral grains…


When magma cools slowly beneath Earth’s
surface, large mineral crystals may form.
These are intrusive rocks.
Extrusive rocks have no visible grains
because they are made from lava that
cooled too quickly for crystals to form.
15) What is porphyritic texture…


Porphyritic texture forms when slowly
cooling magma suddenly cools rapidly.
This forms a rock with large, well-formed
crystals surrounded by finer-grained
crystals of the same mineral.
16) What characteristics of igneous
rocks make them useful…



Interlocking grain textures give them
strength
They are resistant to weathering
Granite is one of the most durable igneous
rocks.
17) Which minerals are often found
in veins of ore?


Gold, silver, lead, copper, and quartz
are often found in veins.
Usually, these veins are found inside
igneous intrusions.
18) What is pegmatite, and give
an example.
 Pegmatites
are veins of extremely
large-grained minerals, such as
garnets, which occur as crystals.
19) What are kimberlites?...
Kimberlites are rare, ultramafic rocks,
which are a variety of peridotite.
They form under very high pressure
and often contain diamonds.
 Ultramafic rocks are very high in iron
and magnesium.
