Pumice is an example of extrusive igneous rock. 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 ...

When you consider plate tectonics we often think of hot magma bubbling up from the Earth’s mantle, and we remember the vast assortment of pictures that we’ve seen–images featuring hundreds of active ...

POTASSIUM–ARGON age determinations have been carried out mainly on minerals with a high potassium content, particularly micas and potassium feldspars, found in intermediate to acid igneous rocks, but ...

You might not know it, but Ireland is dotted with extinct volcanoes that have shaped the island we know and love today ...

What’s hiding inside? Why Wyoming’s Devils Tower is still a geological mystery Standing tall at 1,267 feet in Northeastern ...

Introduction -- Physical properties of magma -- Intrusion of magma -- Forms of igneous bodies -- Cooling of igneous bodies and other diffusion processes -- Classification of igneous rocks -- ...

Devils Tower in Wyoming is surrounded by myths and mysteries. To the Sioux people, this site was sacred and some of their stories tell how this mountain formed: A long time ago a giant bear chased a ...

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, those ...

When driving from Malvern to Hot Springs on U.S. 270, I often take a short detour through one of the most interesting and unusual places in the state: Magnet Cove. Geologist Michael J. Howard has ...