Igneous RocksIgneous Rocks

Properties Properties andand

IdentificationIdentification

Igneous rocks

Mt. Baker is a volcano made of igneous rocks

Igneous - formed by crystallization from

molten magma.

Sedimentary – I like this picture

Rocks of the Vancouver Region

C & T p. 20

Intrusive (Plutonic) Rocks –

•Formed by slow crystallization deepbeneath the Earth’s surface.•Large visible crystals – phaneritic•Identified by mineral content.

Igneous Rocks

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

Golden Ears, Maple Ridge.

Mt. Garibaldi, Squamish.

Colour Index 10% 20% 25% 50% 95%

Quartz

Fine grained (extrusive)

Coarse grained (intrusive)

Rhyolite

Granite

Dacite Andesite Basalt

Quartz diorite

Diorite Gabbro PeridotitePegmatite

Sialic/Felsic (acidic)

Intermediate Mafic Ultramafic (basic)

High Ca, Fe, Mg

High SiO , Na, K

2

Pe

rce

nta

ge

of

Min

era

ls b

y V

olu

me

100

80

60

40

20

0

Orthoclase (K) Feldspar

(Microcline)

Na - rich Plagioclase

(Albite)

Plagioclase Feldspars

Ca - rich plagioclase

Pyroxene (Augite)

Amphibole (Hornblende)

Olivine

MuscoviteBiotite

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 Granite - quartz, orthoclase, plagioclase, hornblende

Diorite - orthoclase (Na & Ca), hornblende Gabbro - orthoclase (Ca), hornblende, pyroxene

Bowen’s Reaction Series

Correlation of Bowen’s Reaction Series with silicon content, viscosity of lava and relative resistance to chemical weathering

Rock Type

Discontinuous Reaction Series

Continuous Reaction Series

Peridotite (Ultramafic)

Gabro & Basalt (Mafic)

Diorite & Andesite (Intermediate)

Granite & Rhyolite (Sialic/Felsic)

Olivine

Pyroxene

Biotite

Am

phibole

Pla

gioc

lase

Fel

dspa

r

Calcium rich

Sodium rich

Orthoclase (K) Feldspar

Muscovite

Quartz

Ord

er

of

Cry

sta

lliz

ati

on

Tem

pe

ratu

re

Sil

ico

n C

on

ten

t

Vis

co

sit

y

Re

sis

tan

ce

to

Ch

em

ica

l W

ea

the

rin

g

H

L H H H

L L L

Volcanic Rocks - Lavas

Rhyolite (high Si) Andesite

Basalt (high Fe) Basalt - vesicular

More Volcanic Rocks

Sodium Feldspar Basalt (Porphyry) Calcium Feldspar basalt (Porphyry)

Obsidian Volcanic Breccia

Volcanic Breccia - Kelowna

Successive eruptions – Coal seams in between!

Volcanic Rocks - Pyroclasts

Pumice Scoria

Welded Tuff Volcanic bomb - olivine core surrounded by basalt