Igneous RocksIgneous Rocks

Rocks Brain-Pop

Igneous RocksIgneous RocksRocks that form when natural, molten rock-

forming material cools and turns into a solid

Igneous Rock Formation Video

Igneous Rock Formation Video

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

Intrusive Igneous Rocks Video

Intrusive Igneous Rocks Video

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

Extrusive Igneous Rocks Video

Extrusive Igneous Rocks Video

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.

Vesicular Rocks - Pumice

Vesicular Rocks - Pumice

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

Magma & Lava VideoMagma & Lava Video

Mt. St. HelensMt. St. Helens

Pre eruption

Post eruption(May 1980)

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