Download Technical Description of a basalt rock Basalt is an extrusive igneous

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Technical Description of a basalt rock
Basalt is an extrusive igneous rock that is fine grained and mafic in composition. Igneous rocks
are classified in two ways: texture and composition.
There are two basalt textures: fine grained and vesicular. Both of these textures are known to
contain phenocrysts (large conspicuous crystals embedded in finer grained textures), dispersed
throughout the rock; both figures 1 and 2 show this feature.
Fine Grained
The crystals that make up basalt rock are so small that they
require magnification to see. Due to the small crystals (grains),
basalt has a smooth look; this texture is also smooth to the
touch. The edges of a basalt rock are angular because of the
way the crystals break when the rock is fractured.
Figure 1: Fine textured basalt.
Vesicular textured rock is rock that cooled with air bubbles
trapped inside. This type of basalt has very small crystals, but
unlike a fine texture, the rock is pitted like a golf ball. The feel
of vesicular basalt is rough due to the various edges exposed
around the air pockets. The pockets decrease the density of
the rock, which makes this type of basalt very light weight.
Figure 2: Vesicular textured basalt
Basalt contains dark minerals, such as pyroxene, olivine, and magnetite. It also contains light
colored quartz and plagioclase. It is composed of more dark minerals containing iron and
magnesium, than light, which give basalt a grey to black color. The iron in basalt is oxidized by
rain, and the color can change to a yellow and red-brown color.
Basalt is prevalent on the surface of the earth, and it is the most abundant igneous rock in the
earth’s crust. This prevalence coupled with basalts’ textures and composition makes it easier to
identify in nature.