chapter 3 section 2 igneous rocks from the core of the continents to nearly all of the oceanic...
TRANSCRIPT
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