Most gemstones form in which part of the Earth's structure?

The formation of most gemstones primarily occurs in the continental crust, which is the thick, buoyant outer layer of the Earth that makes up the continents and continental shelves. This region is characterized by a variety of geological processes that create the conditions necessary for the formation of gemstones.

Gemstones typically originate from specific environments within the continental crust, where factors such as high pressure, extreme temperatures, and the presence of mineral-rich fluids can lead to the crystallization of minerals. For instance, many precious and semi-precious stones, such as diamonds, sapphires, and rubies, form in igneous or metamorphic settings within this layer.

The continental crust is significantly thicker and less dense than the oceanic crust, which makes it more conducive to the development of a diverse range of minerals over geological time. Additionally, the upper mantle, while also instrumental in some types of gemstone formation—particularly in the case of diamonds, which can come from mantle-derived rocks—is not the primary location for the majority of gemstones.

Thus, the continental crust is recognized as the main geological setting for gemstone formation due to its unique conditions that foster diverse mineral development.