Describes magma or igneous rock that is rich in magnesium and iron and that is generally dark in color.

Describes magma or igneous rock that is rich in magnesium and iron and that is generally dark in color.

• A. Mafic
• B. Felsic
• C. Silicates
• D. Porphyritic

Answer: (A)

This question tests how mineral composition relates to color in magma and igneous rocks. Mafic describes rocks that are rich in magnesium and iron, with minerals like olivine and pyroxene. Those ferromagnesian minerals are typically dark, so rocks with this composition usually look dark gray to black. In contrast, felsic rocks are high in silica and light-colored minerals such as quartz and potassium feldspar, giving them a lighter appearance. Silicates is a broad category that includes nearly all igneous rocks, but it doesn’t specify the Mg–Fe richness or color. Porphyritic refers to texture—large crystals in a finer-grained matrix—rather than to chemical composition or color. So, because the clue points to magnesium and iron richness and a dark color, the term that fits best is maf ic.

This question tests how mineral composition relates to color in magma and igneous rocks. Mafic describes rocks that are rich in magnesium and iron, with minerals like olivine and pyroxene. Those ferromagnesian minerals are typically dark, so rocks with this composition usually look dark gray to black. In contrast, felsic rocks are high in silica and light-colored minerals such as quartz and potassium feldspar, giving them a lighter appearance. Silicates is a broad category that includes nearly all igneous rocks, but it doesn’t specify the Mg–Fe richness or color. Porphyritic refers to texture—large crystals in a finer-grained matrix—rather than to chemical composition or color. So, because the clue points to magnesium and iron richness and a dark color, the term that fits best is maf ic.