Answer: The dark color of basalt, a common volcanic rock, is primarily due to its mineral composition. Basalt is rich in iron and magnesium minerals, particularly plagioclase feldspar, pyroxenes, and olivine. The presence of these dark-colored minerals, especially the pyroxenes and olivine, gives basalt its characteristic black to dark green color. These minerals contain iron and magnesium, which are elements that contribute to the dark hues of the rock.
Step-by-step explanation:
Shape: The shape of basaltic rocks can vary widely, from angular fragments in volcanic ash to large, rounded boulders in certain geological formations. However, regardless of their shape, if they contain the characteristic dark minerals, they will appear dark in color.
Size Expansion: The size expansion of basalt does not affect its color. The color is determined by the mineral content, not the size of the rock.
Grain Size: Basalt can have various grain sizes, ranging from fine-grained to coarse-grained, depending on the cooling rate of the lava. However, the grain size primarily affects the texture of the rock (whether it appears fine-grained or coarse-grained) rather than its color.