PowerPoint Presentation Igneous Rocks

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The Rock Cycle- Minerals form rocks All rocks can
be transformed into other rock types Rocks are
divided into 3 categories Igneous-
crystalline- forms as liquid cools
Metamorphic- crystalline-forms as rocks are
heated and squeezed
Sedimentary- non-crystalline- smaller pieces
or chemicals from other
rocks
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Igneous formed from Magma and Lava
Magma

molten rock below Earth's
surface.
L
ava

magma on the Earth's surface.
Pyroclastic material

(
pyro
fire,
clastic
debris)

Airborne lava

cools as it falls
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Composition of the magma

Analogous to what makes up the stew"

What chemical elements are present

What material has the magma moved through

Temperature of the melt

Not only how hot, but how long it stays that hot

also relates to pressure of the molten rock
Cooling environment

fast
vs
slow

Internal vs External
Water content
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Bowen's Reaction Series-
not in your text, but important
Plagioclase
Olivine
(Ca-feldspar)
Pyroxene
Continuous
Discontinuous
Amphibole
Plagioclase
(Na-feldspar)
Biotite
Orthoclase
(K-feldspar)
Muscovite
Quartz
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What things might you describe when looking at an
igneous rock?
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Composition of Igneous rocks
Felsic or Sialic
magma

Si-rich (gt 65)

rich in K, and Al

little Ca, Fe, and Mg.
Intermediate magma

between the two extremes in Si
content and other atoms.
Mafic
magma

Si - poor (lt 35)
richer in Ca, Fe, and Mg.

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Ways of Changing Magma Composition
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Viscosity of Magma/ Lava
Viscosity of Magma/ Lava
Viscosity- important for volcanic activity


the resistance of a liquid to flow


the resistance of a liquid to flow


high viscosity thick and stiff




low viscosity thin and "runny".


Related to
Related to
amount of water (H2O) in magma






amount of silica (Si) in magma



Mafic

Mafic


thin, low viscosity



Felsic

Felsic

thick, high viscosity

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Porphyritic texture
Large white crystals are phenocryts
Aphanitic basalt (mafic composition) constitutes
the groundmass
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Categories of Igneous EOF
Granite
Intrusive rocks

cool beneath Earth's surface

cool very slowly

higher P T

Phaneritic textures
Rhyolite
Extrusive rocks

cool on the Earth's Surface

cool relatively fast

lower T P

Aphanitic textures
Basalt porphyry

Pyroclastic textures
Complex

Partially cools below and above

Porphyritic textures
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Igneous rock names

determined by texture

size and arrangement of mineral grains

AND by mineral composition

minerals affect rock color and indicate
temperature of creation
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Pegmatite

A Pegmatite is a very coarse-grained igneous rock.
Crystals are gt2 cm, often larger.
Most are granitic, although mafic pegmatites can
form.
Biotite mineral grain
Feldspar
mineral
grain
Quartz mineral
grain
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What are the textures in these two rocks ?
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What are the textures in these two rocks ?
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Basalt Gabbro
phaneritic texture
aphanitic texture
forms from mafic magma
forms from mafic magma
Basalt
Gabbro

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Peridotite- the abundance (more than 40) of
Olivine crystals makes the rock take on a green
appearance
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Obsidian- conchoidal fracture And association
with volcanic rocks
Volcanic
Glass
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Tuffs Breccias- look like sedimentary rock
Tuffs Breccias
But they are not.it is volcanic ash that is
lithified
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How do we tell where the igneous rocks formed?
What can we derive from the rocks about the
conditions of formation?
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Pyroclastics
Lava flow
Volcanic neck
Igneous dike
Igneous Sill
Batholith
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Sierra Nevada Batholith- Home to Yosemite
National Park and a lot of Granites and
Grano-diorites
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Sierra Nevada Batholith
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Areal extent of the Idaho Batholith- a huge
(15,400 square miles) intrusive body of primarily
felsic composition (granites) igneous rocks
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An igneous dike- Discordant with surrounding
rock It cuts across other rocks
An igneous sill- Concordant with surrounding
rock It runs parallel to other rocks
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Volcanic Necks Igneous Dikes
Neck
Dike
igneous sill
Igneous sill