How can you identify genuine alexandrite?

Real alexandrite shows a bold colour-change trick, where it goes from greenish or bluish green in daylight to a purplish red when incandescent light is used; also, it tends to sit around a refractive index of 1.746–1.755.

Man-made, colour-change sapphire is frequently marketed as alexandrite, yet the mineral makeup is not the same, and it usually shifts from greyish blue to purple, instead of that classic green-to-red movement. In the case of natural chrysoberyl alexandrite, you can often spot telltale internal features, for example, actinolite crystals or noticeable growth tubes. For a final read, advanced spectroscopic testing confirms the chromium-based atomic structure, without relying on appearance alone.