What qualifies a gem as a natural gem?

A gem qualifies as a natural gem when it is formed through geological processes occurring in nature, without any human intervention. This classification means that the gem has developed over millions of years, undergoing processes such as crystallization and environmental influence in the earth's crust. Natural gems retain their intrinsic properties and character, which can include unique inclusions or variations in color that reflect their natural origin.

Other options pertain to alterations or creations that do not meet the definition of a natural gem. Gems that have been treated to enhance their color, for example, are modified versions of natural stones and do not reflect their original state as they have been influenced by human processing. Similarly, gems created in a laboratory setting under controlled conditions are synthetic and lack the geological history inherent to natural gems. Finally, gems that have been artificially polished have simply been enhanced for appearance but do not affect their classification as natural unless they originate from natural processes.

Thus, the definition of a natural gem is precisely aligned with the description provided in the correct choice.