Igneous

Igneous rocks are made from cooled molten minerals. There are two types of ways lava cools to form igneous rocks: intrusive and extrusive. Intrusive igneous rocks form from magma cooling and hardening under the Earth's surface, while extrusive igneous rocks form from lava cooling and hardening on top of the Earth's surface. The difference between lava and magma is that magma is melted rock below ground, and lava is melted rock above ground. Characteristics of igneous rocks are called properties. Here are a few: If lava cools quickly you can sometimes see air holes in the rock. This property is called vesicular. If an igneous rock contains large cryatals, this is called phaneritic. And the opposite property, aphanitic, means the rock contains crytals that are to small to see with the naked eye. Another property of igneous rocks is mafic. If an igneous rock is mafic, it is dark colored. The opposite of this property is called felsic, meaning the igneous rock is light colored. One final property of igneous rocks is glassy. If lava cools quickly, the rock might gain a shiny luster, creating the property glassy.

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This is pumice, an extrusive, felsic and vesicular Igneous rock.

Wikimedia Image

This is obsidian, an extrusive, mafic and glassy Igneous rock.

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This is granite, an intrusive, felsic and phaneritic Igneous rock.

Flickr Image

Finally, this is rhyolite, an extrusive, felsic and aphanitic Igneous rock.

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