Igneous Rocks Rocks Brain-Pop. Igneous Rocks Rocks that form when natural, molten rock- forming...
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Transcript of Igneous Rocks Rocks Brain-Pop. Igneous Rocks Rocks that form when natural, molten rock- forming...
Igneous RocksIgneous RocksRocks that form when natural, molten rock-
forming material cools and turns into a solid
Liquid (molten) rocks
Liquid (molten) rocks
Lava – On the Earth’s surface (Extrusive)
Magma – Beneath the Earth’s surface (Intrusive)
FormationFormation
Cooling Rates Animation
Solidification – the change from a liquid to a solid
Crystallization – molten magma or lava cools and form solid rocks composed of intergrown mineral crystals
Intrusive Igneous Rocks:
Intrusive Igneous Rocks:
• forms underground• magma never reaches the surface• cools slowly• form large crystals
• medium to coarse grained texture• Get exposed at the surface only when rock is uplifted and exposed
Extrusive Igneous Rocks:
Extrusive Igneous Rocks:
• Forms on the surface
• Lava comes out of a volcano• cools rapidly• forms small crystals
• glassy or fine-grained
• Covers the surface as lava flows or pyroclastic debris
CRYSTAL SIZE VS.
COOLING TIME
CRYSTAL SIZE VS.
COOLING TIME
Crystal
Cooling TIME
SIZE
As cooling time increases, crystal size increases.
FelsicRich in:
• Silica
• Aluminum
• Potassium Feldspar
• Quartz
FelsicRich in:
• Silica
• Aluminum
• Potassium Feldspar
• Quartz
Mafic• Rich in:
• Iron
• Pyroxene
• Olivine
Mafic• Rich in:
• Iron
• Pyroxene
• Olivine
They are classified according to their chemical composition and texture
Classification of Igneous Rocks:
The % of different minerals affect the color of the rock
More silica the lighter the rock, less silica the darker
More Iron the darker the rock, less Iron the lighter
Classify the following rocks as either:Extrusive or Intrusive
Mafic or Felsic
Classify the following rocks as either:Extrusive or Intrusive
Mafic or Felsic
Intrusive + Mafic = Gabbro Extrusive + Mafic = Basalt
Intrusive + Felsic = Intrusive + Felsic = GraniteGranite
Extrusive + Felsic = Extrusive + Felsic = RhyoliteRhyolite
Vesicles (Vesicular) Vesicles (Vesicular)
• As lava rises and cools to form extrusive igneous rock,
• Pressure drops which causes the gases that are in the lava to expand.
• These gases form vesicles (cavities) which are the remains of gas bubbles.
• Intrusive rocks rarely contain vesicles because they are formed at depth where high pressure stops the gases from expanding.
Compare Granite and Basalt
Compare Granite and Basalt
• Granite -
Intrusive (large crystals)
Felsic (Light In Color)
• Basalt -
Extrusive (Small Crystals)
Mafic (Dark In Color)
Crystallization:Crystallization:Crystal Size Animation
• Magma is a mixture of different substances. They all have different melting points.• So as magma cools, some substances will form crystals before other substances. They have a head start in growth and tend to be bigger.•If the magma already has crystals present in it and then is cooled rapidly then you will see large crystals embedded in finer-grained material.
This is called a porphyritic texture
Basaltic lava in HawaiiBasaltic lava in Hawaii
Top: Basaltic lava flow
Bottom: Slow moving lava
Top: Basaltic lava flow
Bottom: Slow moving lava
Igneous Rock ReviewIgneous Rock ReviewIgneous Rock ReviewIgneous Rock Review
1. What is the difference between magma and lava?
2. What are the two main types of igneous rocks?
3. How can you tell them apart?
4. Why is it not common for Intrusive rocks to have vesicles?
Vocabulary: magma, lava, intrusive, extrusive, vesicles, felsic, mafic