Igneous Rock
Igneous rocks (from the Greek word for fire) form from when hot, molten rock (magma) crystallizes and solidifies. The melt originates deep within the Earth near active plate boundaries or hot spots, then rises toward the surface. Igneous rocks are divided into two groups, intrusive or extrusive, depending upon where the molten rock solidifies.
How a Igneous Rock can form
Igneous rocks are called fire rocks and are formed either underground or aboveground. Underground, they are formed when the melted rock, called magma, deep within the earth becomes trapped in small pockets. As these pockets of magma cool slowly underground, the magma becomes igneous rocks.Igneous rocks are also formed when volcanoes erupt, causing the magma to rise above the earth's surface. When magma appears above the earth, it is called lava. Igneous rock are formed as the lava cools above ground.
Intrusive and Extrusive
Extrusive Rock: Extrusive, or volcanic, igneous rock is produced when magma exits and cools outside of, or very near the Earth's surface. These are the rocks that form at erupting volcanoes and oozing fissures. The magma, called lava when molten rock erupts on the surface, cools and solidifies almost instantly when it is exposed to the relatively cool temperature of the atmosphere. Quick cooling means that mineral crystals don't have much time to grow, so these rocks have a very fine-grained or even glassy texture. Hot gas bubbles are often trapped in the quenched lava, forming a bubbly, vesicular texture. Pumice, obsidian, and basalt are all extrusive igneous rocks.
Intrusive Rock
Intrusive Rock: Intrusive, or plutonic igneous rock forms when magma is trapped deep inside the Earth. Great globs of molten rock rise toward the surface. Some of the magma may feed volcanoes on the Earth's surface, but most remains trapped below, where it cools very slowly over many thousands or millions of years until it solidifies. Slow cooling means the individual mineral grains have a very long time to grow, so they grow to a relatively large size. Intrusive rocks have a coarse grained texture.
4 types of Igneous Rock
Basalt-is a fine-grained, dark-colored extrusive igneous rock composed mainly of plagioclase and pyroxene. The specimen shown is about two inches (five centimeters) across.
Gabbro-is a coarse-grained, dark colored, intrusive igneous rock that contains feldspar, augite and sometimes olivine. The specimen shown above is about two inches (five centimeters) across.
Granite-is a coarse-grained, light colored, intrusive igneous rock that contains mainly quartz and feldspar minerals. The specimen above is about two inches (five centimeters) across.
Tuff- is a rock that is composed of materials that were ejected from a volcano, fell to Earth, and then lithified into a rock. It is usually composed mainly of volcanic ash and sometimes contains larger size particles such as cinders. The specimen shown above is about two inches (five centimeters) across.
Pumice-is a light-colored vesicular igneous rock. It forms through very rapid solidification of a melt. The vesicular texture is a result of gas trapped in the melt at the time of solidification. The specimen shown above is about two inches (five centimeters) across.
Gabbro-is a coarse-grained, dark colored, intrusive igneous rock that contains feldspar, augite and sometimes olivine. The specimen shown above is about two inches (five centimeters) across.
Granite-is a coarse-grained, light colored, intrusive igneous rock that contains mainly quartz and feldspar minerals. The specimen above is about two inches (five centimeters) across.
Tuff- is a rock that is composed of materials that were ejected from a volcano, fell to Earth, and then lithified into a rock. It is usually composed mainly of volcanic ash and sometimes contains larger size particles such as cinders. The specimen shown above is about two inches (five centimeters) across.
Pumice-is a light-colored vesicular igneous rock. It forms through very rapid solidification of a melt. The vesicular texture is a result of gas trapped in the melt at the time of solidification. The specimen shown above is about two inches (five centimeters) across.
Links:
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http://www.rocksandminerals4u.com/example_of_igneous_rocks.html
http://geology.com/rocks/igneous-rocks.shtml
http://www.rocksandminerals4u.com/example_of_igneous_rocks.html
Uses of Igneous Rock
Igneous rocks are basically used in flooring, landscaping and construction projects. However, igneous rock uses are specific to its type, which is classified according to the formation process,mineral content, hardness, texture and other properties.