Yes! You guessed it! Igneous rocks are volcanic rocks. And yes there are explosions, but not always. There are two types of igneous rocks, extrusive igneous rocks form after a volcanic eruption out on the Earth's surface, while intrusive igneous rocks form inside volcanos.
TYPES OF IGNEOUS ROCKS FORMING SIDE BY SIDE
Both intrusive and extrusive igneous rocks started in the same place, underneath the Earth's crust. Magma comes from something, and that something is, in fact, a lot of rocks. Inside the Earth, it's extremely hot, too hot for life to survive and even rocks. At a normal 600-1,300˚C inside the Earth, it's hot enough to melt most rocks. Molten (liquid) rock forms when rocks melt. They melt of course, due to the high temperatures, but also the decrease in pressure and form magma. This molten rock cools and solidifies at different locations resulting in two igneous rock types. Factors that form igneous rocks are cooler temperatures and increases in pressure.
INTRUSIVE IGNEOUS ROCKSThey are also known as 'plutonic rocks'. They are named intrusive because they intrude into the Earth's interior.
They form inside the Earth’s crust and mantle from magma surrounded by pre-existing rock (country rock). Intrusive igneous rocks that form at a depth in the crust as termed 'abyssal', while ones that form close to the surface are termed 'hypabyssal.' Intrusive rocks form in the hot magma pockets underground that cool very slowly. The magma can take hundreds, thousands or even millions of years to solidify.
CharacteristicsDue to the slow rate of cooling intrusive rocks are coarse textured, which means that the crystals are large enough to be identified by the naked eye. The slow cooling allows time for the crystals to grow
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Extrusive Igneous Rock Examples:
Scoria, Basalt, and Obsidian Intrusive Igneous Rock Examples:
Granite, Pegmatite, and Gabbro |
EXTRUSIVE IGNEOUS ROCKSThey are also known as 'volcanic rocks'. They are named extrusive because they are extruded out of the Earth's interior.
They form at the Earth's surface through the cooling of lava (referred to a magma when inside the Earth). Magma is brought to the surface through volcanic eruptions or fissures (cracks in the crust). On the crust, lava solidifies and cools at a much quicker rate than intrusive rocks due it being exposed to cool air and water. The lava cools in a matter of days or weeks.
CharacteristicsThe rocks are smooth, shiny, glass-like and fine-grained because the lava cooled too quickly to allow for crystal growth. Extrusive igneous rocks lack crystals, but have a lot of silica in them. Gas bubbles can get trapped in the rock as it cools and solidifies very quickly, leaving holes, giving it a vesicular texture.
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For more examples of igneous rocks, both extrusive and intrusive see: |
CHARACTERISTICS - ALL OF THEM!
Other than the extrusive and intrusive side of igneous rocks, they can also be classified by their colour and crystal size
Igneous rocks have no fossils as the remains will have melted due to the high temperatures inside the Earth. Their colour can be light or dark. If it is dark the rock will have a mafic composition and a high density. On the other hand, if it is light it will have a felsic composition and a low density. Extrusive igneous rocks have gas bubbles such as Scoria. |
TEXTURES AND CRYSTALS
Igneous rocks when extrusive can be glassy, smooth, fine-grained, shiny and lacking crystals or having none at all. Intrusive rocks are instead coarse-grained with large crystals. Texture terms and rocks that have them are listed below:
Igneous rocks when extrusive can be glassy, smooth, fine-grained, shiny and lacking crystals or having none at all. Intrusive rocks are instead coarse-grained with large crystals. Texture terms and rocks that have them are listed below:
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Crystals form in the outer edges of cooling magma. The size of the crystals depends on the magma solidification rate. SLOWER MAGMA COOLING = BIGGER CRYSTALS FASTER MAGMA COOLING = SMALLER CRYSTALS • An extremely fast rate of cooling creates volcanic glass that has no crystals • A slow, then abrupt cooling forms both large and small crystals Examples: Porphyritic Granite, Rhyolite, and Granite
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ECONOMIC IMPORTANCE OF IGNEOUS ROCKS
Earth is predominately composed of igneous rock. Igneous rocks are rich in important minerals and elements including tungsten, tin, iron, uranium, chromium, platinum, strontium, niobium and thorium. The study of the mineral and chemical composition of igneous rocks provides useful information about the temperature and pressure that exists within the Earth’s mantle and crust and its composition and even information about the tectonic environment.