 |
| This photo was taken on one of the lava flows at Cinder Cones
National Natural Landmark in Mojave National Preserve. |
 A dark, fine-grained, extrusive
(volcanic) igneous rock with a low silica content (40% to 50%). Rich in
iron, magnesium, and calcium. Most of the ocean floor is made up of basalt
and it is the most abundant volcanic rock in the Earth’s crust.
 |
| Close-up photo (photomicrograph) of a very thin slice of
basalt. |
The image
at left shows a typical vesicular basalt. Vesicles form
when gas bubbles are trapped in the rock as it solidifies from molten
basalt.
This close-up
photo (photomicrograph) of a very thin slice of basalt was taken through
a microscope with polarized light. Although basalt is a fairly homely
rock to the naked eye, the beauty of its perfectly-formed microscopic
crystals is revealed under the microscope. |
