Igneous Rocks

Topics: Petrology, Igneous rock, Basalt Pages: 3 (835 words) Published: March 1, 2012
Associate Level Material

Comparison Worksheet

Use the following table to compare extrusive and intrusive rocks. Describe and compare each type in at least 150 words.

Extrusive RockIntrusive Rock
Extrusive rocks are also called volcanic rocks and extrusive rocks are formed on the earth’s surface. Extrusive rocks also form from magma, but a form of lava. Magma flows onto the earth’s surface by an eruption by a volcano. When the magma hits the earth’s surface, the magma turns into lava. Extrusive rocks are formed by lava, and the lava will harden quickly and crystallize quickly, either by hot spots or on the earth’s surface. Igneous rocks are considered felsic, intermediate, mafic, and ultramafic. Felsic rocks are high in silica, and usually light colored, and an extrusive rock, which is felsic, is rhyolite. Intermediate rocks are lower in silica content than felsic rocks and an extrusive felsic rock example is andesite. Mafic rocks have a lower silica rate than intermediate rocks, and they are usually dark colored, and an example of an extrusive mafic rock is basalt. Ultrafamic rocks are not generally extrusive rocks, but Peridotite is an intrusive rock, which is ultrafamic.

Intrusive rocks are called plutonic rocks. Intrusive rocks are different than extrusive rocks and are formed underground, by magma, instead of above ground or how extrusive rocks are formed. Magma flows underground and sometimes the magma will stay in places underground and not be erupted by volcanoes. The magma which stays underground will harden for thousands of years, and an intrusive rock is the result, of the hardened magma. Sometimes the intrusive rock will form crystals, which are very visible to the naked eye. Crystals form in intrusive rocks because they cool slowly. Igneous rocks can be felsic, intermediate, mafic, and ultramafic. Felsic rocks are high in silica, and are usually light colored, and an intrusive rock, which is felsic, is granite. Intermediate rocks...
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