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What are extrusive igneous rocks?

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Extrusive igneous rocks form when magma reaches the Earth's surface a volcano and cools quickly. Most extrusive (volcanic) rocks have small crystals. Examples include basalt, rhyolite, andesite, and obsidian. read more

Igneous rocks are formed from the solidification of molten rock material. There are two basic types. Intrusive igneous rocks crystallize below Earth's surface, and the slow cooling that occurs there allows large crystals to form. Examples of intrusive igneous rocks are diorite, gabbro, granite, pegmatite, and peridotite. read more

Extrusive igneous rocks are formed by cooling lava. Since the temperature gradient between lava and Earth’s atmosphere is very big, cooling is very rapid. The second option is deemed true, which also means the third option is false. Foliations occur only in metamorphic rocks, deeming the forth option false. read more

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