Xenoliths
Photo (c) 2008 Andrew Alden, licensed to About.com (fair use policy)
Xenoliths ("ZEEN-a-liths") are rocks brought into a body of lava from outside it—from what geologists call the country rock. The name means "strange stone" in scientific Greek. Nearly everything we know about the rocks of the deep crust, and the Earth's mantle beneath it, comes from xenoliths found in lava. Diamonds come from xenoliths that originated hundreds of kilometers below the ground. But xenoliths might also be bits of a volcano's throat at shallow levels. When limestone, for instance, is engulfed by lava, the results are spectacular metamorphic minerals. This piece of Arizona basalt contains xenoliths consisting of mostly olivine (the green areas) and mostly pyroxene (the black area). The coin is 19 millimeters across.
Fossils
Geologic Features and Processes
Glaciers and Ice
Landforms
Minerals
Rocks
Geology and Society
