Igneous Rocks Rocks Brain-Pop

Igneous Rocks Rocks that form when natural, molten rock-forming material cools and turns into a solid

Igneous Rock Formation Video

Liquid (molten) rocks Lava – On the Earth’s surface (Extrusive) Magma – Beneath the Earth’s surface (Intrusive)

Cooling Rates Animation Formation Solidification – the change from a liquid to a solid Crystallization – molten magma or lava cools and form solid rocks composed of intergrown mineral crystals Cooling Rates Animation

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

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

CRYSTAL SIZE VS. COOLING TIME As cooling time increases, crystal size increases. Crystal SIZE Cooling TIME

Felsic Mafic Classification of Igneous Rocks: They are classified according to their chemical composition and texture Felsic Rich in: Silica Aluminum Potassium Feldspar Quartz Mafic Rich in: Iron Pyroxene Olivine 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 Intrusive + Mafic = Gabbro Extrusive + Mafic = Basalt Intrusive + Felsic = Granite Extrusive + Felsic = Rhyolite

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

Compare Granite and Basalt Intrusive (large crystals) Felsic (Light In Color) Basalt - Extrusive (Small Crystals) Mafic (Dark In Color)

Crystal Size Animation Crystallization: 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 Hawaii Top: Basaltic lava flow Bottom: Slow moving lava

Magma & Lava Video

Mt. St. Helens Pre eruption Post eruption (May 1980)

Vocabulary: magma, lava, intrusive, extrusive, vesicles, felsic, mafic Igneous 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