Igneous Rocks Magma is the molten rock material below the surface. Lower density causes magma to...
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Transcript of Igneous Rocks Magma is the molten rock material below the surface. Lower density causes magma to...
Igneous Rocks
Magma is the molten rock material below the surface.
•Lower density causes magma to rise toward the surface (compared to the surrounding rock).
•Magma at the surface is lava.
•Igneous rocks are formed from solidified/cooled magma or lava.
•Igneous rocks are made of interlocking crystals
Igneous RocksMagma extruded onto the Earth’s surface forms volcanic or extrusive igneous rocks.
Magma that crystallizes within the Earth’s crust forms plutonic or intrusive igneous rock.
Extrusive & Intrusive Igneous Rocks
• Intrusive- Magma under the surface– Coarse-grained (igneous rock)– Magma cools slowly and large crystals grow over a long period of time
– Gabbro, diorite, granite
Extrusive & Intrusive Igneous Rocks
• Extrusive- Lava at the surface– Fine-grained (igneous rock)– Lava cools very quickly, consequently crystals do not have time to grow and develop
– Basalt, andesite, rhyolite, obsidian
Igneous Rocks
Molten rock or magma(1,000-1,200 oC), contains chemical elements.
If the magma begins to cool, elements begin to form chemical bonds within the magma and crystals start to develop.
Igneous RocksThe crystallization of magma fluids, either through extrusive or intrusive processes, creates the minerals that make up igneous rocks.
All rocks are composed of minerals, and minerals are composed of one or more chemical elements.
Igneous RocksThe primary elements that make up rock-forming minerals are: -Silicon (Si)-Oxygen (O)-Iron (Fe)-Magnesium (Mg)-Potassium (K)-Sodium (Na)-Calcium (Ca) Various combinations of these elements form the most common mineral group, the silicates. The most important silicate minerals are quartz, feldspar, mica, amphibole, pyroxene, and olivine.
Igneous Rocks
As magma cools slowly, elements within it become chemically bonded forming crystals of minerals.
However, not all minerals form at the same time during the cooling process. Some minerals crystallize when magma is at a higher temperature, while others only crystallize when magma is at a lower temperature.
Bowen's Reaction Series describes when the eight most common silicate minerals form during the cooling process.
Igneous Rocks
Rocks that form from magma or lava cooled from high temperatures tend to contain a lot of iron and magnesium but little silica. These rocks are called mafic and tend to be dominated by dark colored minerals such as amphibole and pyroxene (Elements: iron & magnesium).
Igneous Rocks
When magma cools slowly, minerals that form at cooler temperatures dominate the resulting rock. These rocks are called felsic and tend to be light colored with minerals such as feldspar and quartz. (Elements: silicon, oxygen, sodium, potassium, & aluminum)
Igneous Rocks
Granite•Felsic•Intrusive
Igneous Rocks
Other Igneous Rocks• Lava flows• Fragmented magma ejected explosively– Ash plumes– Pyroclastic flows
• Cool and solidify very quickly; no minerals developConsequently they cannot be mafic, intermediate, or felsic