Which type of gem is described as idiochromatic?

Idiochromatic gems are characterized by having their color derived from the elements that are inherently part of their chemical structure. This means that the color is not influenced by external factors, such as impurities or alterations in the environment, but rather is a direct result of the specific elements and their interactions within the gemstone itself.

For example, a mineral like emerald is idiochromatic because its green color is due to the presence of chromium or vanadium within its chemical makeup. These elements are integral to the formation of the emerald, resulting in its distinct coloration. This intrinsic property distinguishes idiochromatic gems from other types, such as allochromatic gems, which gain their colors from trace elements or impurities rather than from their own composition.

Understanding this distinction helps in identifying and categorizing different gemstones based on their formation and the reasons behind their colors, which is essential knowledge for anyone studying colored stones.