CHAPTER 3 SECTION 2 IGNEOUS ROCKS From the core of the continents to nearly all of the oceanic crust—igneous is everywhere!

CHAPTER 3 SECTION 2 IGNEOUS ROCKS

From the core of the continents to

nearly all of the oceanic crust—igneous is everywhere!

IGNEOUS ROCKS

Formed from cooled/hardened _________ or ______ Are called _______________ [ignis Latin fire] The rate of __________ determines the size of the

mineral’s crystals.

“fire” rocksmagma lava

cooling

andesite

basaltpumice

INtrusive: below groundcools slower many many & large crystalsEx: granite, gabbro

Intrusive Igneous Visible due to erosion & weathering Magma= mainly silicon & oxygen

• Gases: water vapor (gases trapped) Magma less dense than surrounding

rock moves towards surface & cools• Elements combine minerals form &

‘grow’ crystals! Example:

Granite Cumberlandite

Intrusive Igneous: Cumberlandite

Only found in Cumberland, RI (official state rock)• 4-acre lot in Blackstone Valley (Iron Mine Hill) & trace

amts. Narr. Bay Dense & prone to rust (iron magnetic); titanium,

transitions to peridotite (intr. coarse ign.) Formed 1.5 bya volcanic activity Valuable cannon and farm tools 18th/19th cent.

Obsidian

Air bubbles are sometimes trapped (pumice, scoria)

Basalt

EXtrusive: above ground cools quicker f e w & small crystals

Extrusive Igneous Magma = below ground// Lava=

above ground• Lava most gases escaped

Lava hardens extrusive igneous rock• Extruded onto surface• Example: Rhyolite, Basalt

Basalt

Classifying Igneous Rocks Classification based

on two major characteristics:1. Texture: appearance

based on size, shape & arrangement of crystals

2. Composition: proportions of light and dark minerals

Classification: Texture Coarse-grained: slow cooling large crystals

Allows charged atoms (ions) to move large distances within magma & link together (crystallize)

Fine-grained: rapid cooling small crystals Ions lose motion and quickly combine; all compete for available ions

Glassy: lava on surface little time for ions to crystallize randomly distributed glassy appearance (tiny crystals)

Porphyritic: different-sized minerals experience different rates of cooling

• Large crystals (phenocrysts) may be surrounded by fine grained minerals• Minerals don’t crystallize @ same rate (location and melting point.)

Classification: Composition Granitic: light-colored silicates (quartz & feldspar)

• 70 % silica• 10 % dark silicate minerals (i.e. biotite mica, amphibole)• Major component of continental crust• Ex: rhyolite = extrusive granitic rock

Basaltic: contain many dark silicate materials (plagioclase feldspar)• Rich in magnesium and iron

Iron darker and denser than granitic rocks• Ex: gabbro = intrusive basaltic rock

Andesitic: composition between granitic and basaltic• Volcanic rock = andesite:

At least 25 % dark silicates (amphibole, pyroxene, biotite mica) Dominant mineral plagioclase feldspar :type of feldspar dark

w/ridges (striations) Ultramafic: composed almost entirely of dark silicate minerals

• Rare @ Earth’s surface Ex: peridotite—upper mantle composition