4 Liquid (molten) rocks Lava – On the Earth’s surface (Extrusive) Magma – Beneath the Earth’s surface (Intrusive)
5 Cooling Rates Animation FormationSolidification – the change from a liquid to a solidCrystallization – molten magma or lava cools and form solid rocks composed of intergrown mineral crystalsCooling Rates Animation
6 Intrusive Igneous Rocks: forms undergroundmagma never reaches the surfacecools slowlyform large crystalsmedium to coarse grained textureGet exposed at the surface only when rock is uplifted and exposed
10 CRYSTAL SIZE VS. COOLING TIME As cooling time increases, crystal size increases.CrystalSIZECooling TIME
11 Felsic Mafic Classification of Igneous Rocks: They are classified according to their chemical composition and textureFelsicRich in:SilicaAluminumPotassium FeldsparQuartzMaficRich in:IronPyroxeneOlivineThe % of different minerals affect the color of the rockMore silica the lighter the rock, less silica the darkerMore Iron the darker the rock, less Iron the lighter
12 Classify the following rocks as either: Extrusive or Intrusive Mafic or Felsic Intrusive + Mafic = GabbroExtrusive + Mafic = BasaltIntrusive + Felsic = GraniteExtrusive + Felsic = Rhyolite
13 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.
17 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
23 Mt. St. HelensPre eruptionPost eruption(May 1980)
24 Vocabulary: magma, lava, intrusive, extrusive, vesicles, felsic, mafic Igneous Rock Review1. 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
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