Which mineral primarily composes the upper mantle of the Earth?

The upper mantle of the Earth is primarily composed of olivine, a magnesium iron silicate mineral. This mineral is significant for several reasons. First, it has a high melting point and is stable under the high-pressure conditions found in the Earth's upper mantle, which extends from about 7 to 400 kilometers beneath the Earth's surface. Olivine is also a major component of peridotite, the rock type most commonly found in the upper mantle.

Moreover, olivine's crystal structure allows it to accommodate various compositions, making it a key player in the dynamics of mantle convection and the generation of magma. Its presence influences the physical properties of the mantle, including its viscosity and the types of magmas produced when mantle material melts and rises to the surface.

The other minerals listed, such as quartz, granite, and basalt, are primarily associated with the Earth's crust rather than the mantle. Quartz is a common mineral in the continental crust, granite is an intrusive igneous rock composed mainly of quartz and feldspar, and basalt is a volcanic rock that predominantly forms the oceanic crust. Therefore, they do not make up the upper mantle significantly, confirming that olivine is indeed the primary mineral found in this region.