Alexandrite one of the varieties of chrysoberyl

Alexandrite one of the varieties of chrysoberyl.

A special case among the colored gemstones is alexandrite, one of the varieties of chrysoberyl. Pure chrysoberyl is a double metal oxide with the chemical formula BeAl2O4. This formula can also be written differently: BeO · Al2O3, a mixture of beryllium oxide and alumina. Like many gemstones we already know, pure chrysoberyl is colorless, not very showy, uninteresting for jewelers. Alexandrite is chrysoberyl contaminated with oxides of two different metals - chromium oxide red in color and iron oxide in green. The unexpected effect of this double contamination is a deep green color in daylight, changing to raspberry red or purplish red under artificial light from an incandescent lamp.

After reading the messages preceding the sentence above, everyone should find the answer to the next question on their own: why. Why does alexandrite change its colors depending on the type of lighting?. One more piece of information can be added to make it easier. Illuminated by white light emitted by "glowing cold"” fluorescent lamp, alexandrite remains green. I think, that we know everything now. Daylight and fluorescent light are white light made up of all the basic components of the spectrum. Meanwhile, the bulb is not a body heated to a very high temperature, so it emits light with a different composition, closer to the red part of the spectrum than sunlight, thus other components of the spectrum are absorbed by alexandrite and the others constitute the complementary color.