KEY POINTS IN THIS CHAPTER •
Igneous rocks are mostly silicates that are born out of magma.
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The silica content and the cooling rate both affect what the end state of the rock looks like.
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Magma is on a continuum ranging from mafic type, which is silica-poor, to felsic, which is silica-rich.
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The type of rock you see depends on chemical reactions taking place between the atoms of iron, magnesium, aluminum, sodium, and potassium and the silica tetrahedron.
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Igneous rock can be intrusive, made within the earth, or extrusive, cooled external to the earth's surface.
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Magma rises to the surface to make sills, dykes, laccoliths, and other formations coming up from plutons rising out of magma pools and settling into layers of sedimentary rock.
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Diamonds are carbonaceous and made from very deep parts of the earth.
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