Buoyancy The driving force of most geological processes on Earth is density and buoyancy due to chemical properties of minerals. The most important way to classify minerals is by chemical composition. According to Britannica, silicate minerals make up over 95% of all the minerals in the crust and mantle. At one end of the spectrum of silicate minerals are mafic minerals, and at the other are felsic minerals. Mafic minerals are named so because they typically contain high amounts of magnesium and iron, and comparatively low amounts of silicon. Felsic minerals are the opposite, containing high amounts of silicon and low amounts of iron and magnesium. The reason this distinction is important is because the mafic minerals are typically much more dense than felsic minerals. As a result of this distinction, mafic and felsic minerals are segregated by density into the generally mafic mantle and the generally felsic crust. In this regard, the crust can be thought of as floating on top of the mantle because of its lower density. According to Nullet this floating action leads to scenarios in the crust such as subduction, where the heavier oceanic crust sinks under the lighter continental crust at plate boundaries. Another property of the earth that arises as a result of buoyancy is convection of the Earth’s magma. In convection, the hotter, deeper and less dense fluids of a system rise to the top, force cold fluid down, cool off, and sink back down. This cycle repeats and forms currents in the system. Convection of magma causes the tectonic plates on the earth to move, and creates situations in the earth’s crust such as sea floor spreading and rift valleys. Because of the spreading action, new materials are brought up from the mantle to fill the gap, making the oceanic crust mafic and leading to subduction at oceanic-continental boundaries.