Bubbling basalt!
 As you walk along the trail toward Sunset Crater Volcano everywhere
you look you'll see black, bubbly basalt. Basalt is the most common volcanic
rock you'll see on the Earth’s surface. When most people think of
lava
or what is generally called 'lava rock', they are usually thinking of
basalt.
Basalt, like all volcanic rocks, starts as hot lava that erupts
at or near the Earth’s surface. Once it’s outside, contact with the atmosphere
or water cools the hot lava very quickly. Quick cooling prevents minerals
from growing to a large size. That’s why basalt and other volcanic rocks
are made mostly of tiny mineral grains that can only be identified with
a microscope.
The first thing people most people notice about basalt is its
very dark color. Basalt has lots of iron and magnesium-rich minerals that
give it its distinctive, almost black color. Despite basalt’s dark color,
the single most abundant material (40-50%) in it is silica,
the stuff that window glass is made of.
 The second thing people most people notice about basalt along
the Lava Flow trail is its bubbly texture. Geologists call these small
bubbles vesicles. They can be found in any type of volcanic rock. Vesicles
are evidence that the basaltic lava had plenty of gas. Given enough time,
the gas will its way out of the lava and escape into the air. These gas
bubbles were frozen into place before they could escape. |
