basalt

   It's one of our favorite rocks.  It is usually very picturesque, and gives one the impression of a "coating", which it usually is.
   Basalt is a dark to black igneous rock, fine-grained, and heavy.  It is very hot when molten, and flows readily, creating vast areas covered with lava layers.
   The "drippy" looking black rubble coming off the hills and mesas along the Black Canyon Freeway north of Phoenix is basalt.  It erupted from deep cracks in Earth's crust, and flowed out to cover the landscape about 16 million years ago.   This basalt is some of the youngest rock visible around Phoenix.
   The dark spots you see when you look at the face of the moon -- all those flat featureless plains that were once thought to be oceans -- are basalt.
   The Hawaiian Islands are a product of the great mid-Pacific volcanoes like Mauna Kea, and they are made of basalt.  And the barren plains of southern Idaho and eastern Washington are resting on basalt flows that possibly resulted from an ancient asteroid impact.

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