We often talk about climate change, melting glaciers, or strange landforms. But we rarely think about something that’s always ...

The word extrusive means that the magma was forced onto the earth's surface and cooled in a matter of hours. Granite is an example of intrusive igneous rock.

Extrusive igneous rocks are formed by magma that has erupted onto the surface as lava and then cooled quickly. Obsidian is an example of an extrusive igneous rock.

Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive ...

1. Igneous rocks: They are formed, when the molten magma cools and becomes solid. There are two types of igneous rocks: intrusive rocks and extrusive rocks.

Basalt is what’s known as an extrusive igneous rock - it is volcanic, formed from molten magma that extruded onto the Earth’s surface and hardened. It is dark in color and heavy and dense.

In my last column, I wrote about the locations where you can find igneous rocks that were formed from lava. The metarhyolite and metabasalt described in the column are known as extrusive rocks ...

O. F. Tuttle, Origin of the Contrasting Mineralogy of Extrusive and Plutonic Salic Rocks: A Reply, The Journal of Geology, Vol. 61, No. 3 (May, 1953), pp. 278-280 ...