Igneous Rocks Intrusive and extrusive rocks formed from
- Slides: 36
Igneous Rocks Intrusive and extrusive rocks formed from the cooling and crystallization of magma.
Magma vs. Lava • Magma is molten rock beneath Earth’s surface • Lava is magma that has flowed out onto Earth’s surface
Two types of Igneous Rocks Extrusive Igneous Rocks • Fine grained igneous rocks that cool quickly on the Earth’s surface(forms from Lava). Ex. Rhyolite Intrusive Igneous Rock • Course grained Igneous rock that cools slowly beneath the Earth’s surface(forms from magma). Ex. granite
Rhyolite- extrusive rapid cooling
Granite- Intrusive slow cooling
Composition of Magma • A slushy mix of : Molten rock Gases Mineral crystals
Elements in Magma • • Oxygen (O) Silicon (Si) Aluminum (Al) Iron (Fe) • Potassium (K) • Sodium (Na) • Magnesium (Mg) • Calcium (Ca)
• Magma is classified based on the amount of silica it contains. Si. O 2
Types of magma Group Si. O 2 Content • Rhyolitic • Andesitic • Basaltic 70% 60% 50%
Origins of Magma • In labs, most rocks melt when they hit 800°C to 1200°C • These temps are found in the upper mantle & lower crust • Scientists think this heat comes from the decay of radioactive elements & the remaining energy from Earth’s molten formation •
Check Point 1. What is the difference between magma and lava? 2. What are the two types of igneous rocks? 3. Which type of magma has the most silica content?
Factors That Affect Magma Formation 1. Temperature – Temp ↑ with depth in Earth’s crust 2. Pressure – Pressure ↑ with depth because of the weight of overlying rock – As pressure ↑, so does the melting point
3. Water content – Rocks & minerals contain little water – The higher the water content , the lower the melting point 4. Mineral’s composition – Different minerals have different compositions and therefore have different melting points
How Rocks Melt • Partial Melting – process in which different minerals melt into magma at different temperatures, changing its composition. – Some minerals melt, while others remain solid – As minerals melt, different elements are added to the magma “stew, ” thereby changing its composition
• Fractional Crystallization – process in which different minerals crystallize from magma at different temperatures, removing elements from magma. – Changes composition of magma by removing elements
Bowen’s Reaction Series • Discovered by a geologist named Bowen • Sequential, predictable, dual-branched pattern in which minerals crystallize from cooling magma Two main patterns or branches of crystallization 1. Continuous, gradual change of mineral composition • Ex. feldspars (change from calcium rich to sodium rich)
• Magma is made up of different minerals that crystallize at different temperatures. • So during the cooling and crystallization process some minerals become solid while others remain molten.
Bowen’s Reaction continued… 2. An abrupt change of mineral type Iron-rich minerals change into other minerals. Ex. At 18000 C Olive forms once that substance reaches 1557 degrees a new mineral is formed (pyroxene).
Magmatic Differentiation • As minerals form in the Bowen series the solid more dense ones fall to the bottom and are not available for the reaction anymore so the material that is available is now different.
Bowens reaction https: //www. youtube. com/watch? v=K 6 a. Ql. Y A 4 BHU • www. youtube. com/watch? v=R 4 X 8 uk. Spb. Q o • https: //www. youtube. com/watch? v=Ap. Lp 7 GMDOE 0
Crystal separations • Under certain conditions newly formed crystals can be separated from rock that explains why olivine is found in the rock that is why olivine did not convert to pyroxene during cooling.
Layered Intrusions • Sometimes during cooling layered intrusions form. Scientist are uncertain why. Maybe temperature differences. Valuable rare metals maybe found here. Ex. Platinum, chromium, nickel, and gold.
Check Point 1. What happens to temperature with depth? 2. As depth increases does pressure decrease or increase? 3. What is partial melting? 4. Summarize Bowen’s reaction?
5. 2 Classifying Igneous Rocks • Igneous rocks are broadly classified as intrusive or extrusive. • However, they are further classified by – mineral composition • what minerals are found in the rock – color – grain size
• if lava cools quickly then small crystals form Example: Obsidian has no visible mineral grains • if magma cools slowly then large crystals form Example: Gabbro has large mineral grains
– texture • early forming minerals may have well shaped crystals • later forming minerals may have irregular shaped crystals • porphyritic texture – contains both large & small crystals •
Classification of Igneous Rocks
Four Main Groups of Igneous Rocks 1. Felsic – Light colored – High silica content – Contain quartz, feldspar, orthoclase, and plasioclase – Ex, granite
2. Mafic –Dark colored –Low Silica –Plagioclase, biotite, amphibole, pyroxene, and olivine –Rich in Iron and Magnesium –Example, Gabbro
3. Intermediate • page 107 Contain moderate amounts of biotite, amphibole, pyroxene, and olivine. • Ex. diorite
4. Ultramafic –Low Silica –High Iron and Magnesium –Ex, Peridotite and dunite
Check Point • What are the four mineral composition types and two facts about each? (you have 5 minutes) • What is a pegmatite? • What is a kimberlite? • Answer #6 on p. 106
Igneous Rocks as Resources Igneous rocks are good resources as building materials because of their strength, durability, ability to resist weathering, and beauty.
Ore Deposits Ore deposits can be found within igneous rocks or in the cracks and voids surrounding the rocks, called veins – Dissolved silica & common metals (Ex: gold, silver, lead, copper) are released at the end of magma crystallization in a hot, mineral rich fluid that fills the veins. – Fluid solidifies to form metal-rich quartz veins – Ex, gold-bearing quartz in Sierra Nevada Mountains in California
• Pegmatite- vein deposits of extremely large-grained minerals that can contain rare ores such as lithium and beryllium • Kimberlites – rare, ultramafic rock that contain diamonds and other minerals formed only under very high pressures • •
- Types of rocks metamorphic
- Rocks formation
- Intrusive vs extrusive igneous rocks
- Extrusive igneous rocks
- Extrusive igneous rocks example
- Sedimentary deposition
- Metamorphic rocks
- Igneous rocks metamorphic rocks and sedimentary rocks
- Non banded rocks
- Pumice extrusive or intrusive
- Intrusive rocks
- What is igneous rock
- How igneous rocks are formed
- Igneous rock
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- How is igneous rock classified
- Is obsidian intrusive or extrusive
- Mafic extrusive igneous rock
- Mafic extrusive igneous rock examples
- How igneous rocks are formed
- How igneous rocks are formed
- How are igneous rocks formed
- What are underground igneous rock bodies called?
- Magma defintion
- Rock type
- Parent rocks
- Concept map for igneous rocks
- What are massive igneous rocks
- Three types of rocks
- Igneous rocks concept map
- Relative age of rocks diagram
- Pumice crystal size
- Characteristics of igneous rocks
- Concept map for igneous rocks
- Iugs classification of igneous rocks
- Sedimentary rocks examples
- Igneous rock texture