Final answer:
The dark-colored (mafic) silicate mineral common in Earth's mantle and oceanic crust is olivine. It is rich in iron and magnesium, which contribute to its characteristically darker color. Gabbro and basalt are examples of mafic rocks that commonly contain olivine.
Step-by-step explanation:
The dark-colored (mafic) silicate mineral that is common in Earth's mantle and oceanic crust is olivine. Unlike quartz, feldspar, and mica, olivine is rich in iron and magnesium, which contributes to its darker color and higher density. These characteristics are typical of mafic minerals, which are predominant in the mantle and the oceanic crust.
Mafic rocks such as gabbro or basalt often contain olivine, as well as pyroxene and Ca-rich plagioclase. In contrast, felsic rocks, like granite and rhyolite, typically feature lighter-colored minerals like quartz and potassium feldspar. The color of igneous rocks, influenced by their mineral content, is therefore a useful diagnostic tool for identifying the type of rock and the minerals present within it.