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Igneous...ignite! And that's just what happens when igneous rocks form. Fiercely hot [link widoczny dla zalogowanych] molten rock from deep inside the earth pushes its way out and lights everything in its path on fire. As the firey liquid cools, it forms igneous rocks.
Rock types are organized, or classified, according to how the rock [link widoczny dla zalogowanych] formed. It's a [link widoczny dla zalogowanych] pretty simple system and there are only three types: igneous, sedimentary and metamorphic. Their names give clues about how the rocks were formed.
Earth's Mantle
Under the [link widoczny dla zalogowanych] crust is the fiery hot mantle. Saying [link widoczny dla zalogowanych] that the mantle is fiery hot does it injustice. The coolest outer part of the [link widoczny dla zalogowanych] mantle is about 1000 degrees Celsius (1800 degrees Fahrenheit). Here the rock is molten liquid, white hot.
All Magma is made up of a fairly uniform mixture of elements. Some of the major elements present are silica, iron, sodium, potassium, aluminum, magnesium, and [link widoczny dla zalogowanych] gasses including water vapor, oxygen, carbon dioxide, nitrogen, hydrogen [link widoczny dla zalogowanych] and sulfur dioxide. These elements form chemical combinations that crystallize in patterns to form eight basic rock forming minerals. These eight minerals form most rock. They are olivine, pyroxene, amphibole, orthoclase, plagioclase, muscovite, biotite, and quartz.
Igneous Rock Formation
Igneous rocks are formed from this molten magma. These rocks form when the magma cools and [link widoczny dla zalogowanych] crystallizes. This can happen above ground as with volcanoes it is then called extrusive.
There are many kinds of volcanoes around the world. The materials that come from a volcano are different as well. We tend to lump them all under the term lava but rocks ranging from the very dense basalt to the very light pumice are just a part of what can come from a volcano. There is also ash, volcanic glass or [link widoczny dla zalogowanych] obsidian, and the gem stone peridot to name a few.
The molten magma can also crystalize below the surface. When the molten rock rises in the crust but cools before it reaches the surface it is plutonic igneous rock and is categorized as intrusive.
Cool Enough
When the magma reaches the surface it cools quickly, a matter of days or weeks.
When the magma forms pockets [link widoczny dla zalogowanych] underground it cools much more slowly. This could take thousands or even millions of years.
The rate at which the magma cools determines the kind of rocks that are formed. Faster cooling surface lava creates rock that is fine grained or aphanitic. The rapid cooling doesn't allow large crystals to form. I addition most of the gasses are driven off into the atmosphere.
The slower cooling that takes place underground allows larger crystal formation. Granite is an example of this type of rock formation.
Other igneous rocks are pumice, scoria, gabbro, basalt, ryolite, dacite, andesite and obsidian.
Rocks are, after all, the history books of the earth's extremely long life. The conditions during the formation left marks that one can learn to read, thereby discovering [link widoczny dla zalogowanych] what happened to make a particular kind of rock in a particular place at a particular time.
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