Rocks from the continental crust
Continental crust is significantly thicker than oceanic crust. It stands higher and penetrates deeper into the mantle than its oceanic counterpart. The upper continental crust is exposed at many places, and its composition is well known. The lower continental crust is not exposed; geologists learn about it by studying how shock waves from earthquakes and man-made explosions pass through it, and by examining the rare fragments carried to the surface by erupting lavas.
Topic: Earth Sciences
Subtopic: Earth Structure
Keywords: Continental crust, Geology, Earth (Planet)--Crust, Rocks, Earthquakes
Sedimentary rocks form a thin veneer over much of the crust.
The upper crust is made of low-density granitic rocks.
Dense metamorphic rocks, such as granulite and gneiss, make up most of the lower crust.
This rare sample, also from the deep crust, contains tiny red garnets and dark green pyroxene that formed at 50 to 60 kilometers below the surface, at 600 degrees Centigrade.