What is a color change in gemstones?

A color change in gemstones refers specifically to a distinct change in a gem's color when viewed under different lighting conditions. This phenomenon is most commonly associated with certain minerals, such as alexandrite and color-change spinel, which exhibit different hues when viewed in natural daylight compared to incandescent light. The ability to observe this change is an important characteristic and contributes to the gem's uniqueness and desirability.

Different lighting types can alter the appearance of a gemstone because the light spectrum in each setting can enhance or diminish certain wavelengths of color. For instance, a gem that looks green in daylight might appear more purple in incandescent light. This color shift is a fascinating optical property that gemologists and collectors value, and it plays a crucial role in how these stones are evaluated.

The other choices pertain to different concepts: a modification in chemical composition relates to the gem's material characteristics rather than its visual properties; a grading system for gem color refers to the standardized methods of evaluating color quality; and methods for identifying gem authenticity involve various techniques to verify whether a gemstone is natural or synthetic. Each of these aspects plays a role in gemology, but they don't directly define the intriguing phenomenon of color change.