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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. TEXTURE 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. Vesicular 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 COMPOSITION 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. CONCLUSION 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.