Visual Glossary Of Geologic Terms Basalt

Basalt 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 This photo was taken and it is the most abundant volcanic on one of the lava flows rock in the Earth’s crust. at Cinder Cones National Natural Landmark in Mojave National Preserve.

The image at left shows a typical vesicular basalt. Vesicles form when gas bubbles are trapped in the rock as it Close-up photo solidifies from molten basalt. (photomicrograph) This close-up photo (photomicrograph) of of a very thin slice of basalt. Click a very thin slice of basalt was taken here to see entire through a microscope with polarized light. slide. Although basalt is a fairly homely rock to the naked eye, the beauty of its perfectly-formed microscopic crystals is revealed under the microscope.