Answer:
Iron and magnesium
Explanation:
Igneous rocks are commonly classified by their composition and texture, they are formed in the Earth's crust and therefore, they are mostly made up of silicate minerals.
These silicates can be generally divided into light and dark silicates:
- The light-colored silicates include quartz, muscovite, and feldspar.
- The dark silicates, also called ferromagnesian or mafic because of the presence of iron and magnesium in them, include olivine, pyroxene, amphibole, and biotite. They are dark green, gray, or black and have greater specific gravity (between 3.2 and 3.6) than do non-ferromagnesian silicates
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