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Igneous Rocks
Properties
and
Identification
Igneous - formed by
crystallization from
molten magma.
Igneous rocks
Sedimentary –
I like this picture
Mt. Baker is a volcano made of
igneous rocks
Rocks of the Vancouver Region
C & T p. 20
Igneous Rocks
Intrusive (Plutonic) Rocks –
•Formed by slow crystallization deep
beneath the Earth’s surface.
•Large visible crystals – phaneritic
•Identified by mineral content.
Golden Ears, Maple Ridge.
Extrusive (Volcanic) Rocks Formed by rapid crystallization on
the Earth’s surface
Crystals only visible under a
microscope - aphanitic
Identified by mineral content and
structure
Mt. Garibaldi, Squamish.
Igneous Rocks Mineral Content
Plutonic Rocks - Structure of Granite
Polished granite section illustrating the mixture of large crystals of different minerals
(q = quartz, af = albite feldspar, b = biotite mica
Plutonic Rocks
Granite - quartz, orthoclase, hornblende
Diorite - orthoclase (Na & Ca), hornblende
Granite - quartz, orthoclase, plagioclase, hornblende
Gabbro - orthoclase (Ca), hornblende, pyroxene
Bowen’s Reaction Series
L
L
Silicon Content
Viscosity
L
H
H
L
Fe
lds
pa
r
gio
c
la s
e
Orthoclase
(K) Feldspar
Muscovite
Quartz
Resistance to Chemical Weathering
(Sialic/Felsic)
H
Temperature
Granite &
Rhyolite
Sodium
rich
Order of Crystallization
(Intermediate)
tit e
Bio
le
ibo
ph
Am
Diorite &
Andesite
e
en
(Mafic)
rox
Py
Gabro &
Basalt
Calcium
rich
ne
iv i
(Ultramafic)
Continuous
Reaction Series
Ol
Peridotite
Discontinuous
Reaction Series
Pla
Rock
Type
H
Correlation of Bowen’s Reaction Series with silicon content, viscosity of lava
and relative resistance to chemical weathering
Volcanic Rocks - Lavas
Rhyolite (high Si)
Basalt (high Fe)
Andesite
Basalt - vesicular
More Volcanic Rocks
Sodium Feldspar Basalt (Porphyry)
Obsidian
Calcium Feldspar basalt (Porphyry)
Volcanic Breccia
Volcanic Breccia - Kelowna
Successive eruptions – Coal seams in between!
Volcanic Rocks - Pyroclasts
Pumice
Welded Tuff
Scoria
Volcanic bomb - olivine core surrounded by basalt