Final answer:
The igneous rock with the least amount of silica is referred to as a mafic rock. These dark-colored rocks are rich in iron and magnesium and include minerals like pyroxene and olivine, as opposed to the lighter-colored, silica-rich felsic rocks.
Step-by-step explanation:
The type of igneous rock that would have the least amount of silica is known as mafic rock. Mafic igneous rocks are rich in magnesium and iron, and they typically have dark colors due to the presence of minerals like pyroxene and olivine. In contrast, felsic rocks, which are high in silica, contain minerals such as quartz and feldspar and are typically lighter in color.
Igneous rocks are categorized based on their mineral content and the size of their grains. The rapid cooling of lava on the Earth's surface results in rocks with fine grains, which are extrusive or volcanic in nature. Conversely, slow cooling within the Earth creates rocks with larger, coarse grains, known as intrusive or plutonic rocks. When identifying igneous rocks, color is a helpful guide: dark-colored rocks like basalt, which are fine-grained and contain fewer silicate minerals, are indicative of mafic rocks, while light-colored rocks are usually felsic and silica-rich.