In what type of environment does turquoise typically form?

Turquoise typically forms in an arid and semi-arid environment, which is often characterized by the presence of copper-bearing minerals and the necessary geochemical conditions for its formation. The correct answer reflects that turquoise is commonly found in areas that have experienced significant weathering and alteration of minerals in a dry climate, rather than within metamorphic rocks like marble or quartzite, or in volcanic settings.

In such environments, the conditions allow for the leaching of copper, aluminum, and phosphorus, which combine to form turquoise. Understanding this context helps in identifying the geological factors that contribute to the formation of this unique gemstone. Other listed environments do not possess the specific conditions required for turquoise formation, reinforcing why the selected answer accurately aligns with the known geological characteristics of turquoise deposits.