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Alexandlite
| Chemical Formula | BeAl2O4 |
| Mohs Hardness | 8.5 |
| Specific gravity | 3.7 |
| Description |
Alexandrite is the highly regarded color changing variety of Chrysoberyl. The color of Alexandrite changes under different lighting conditions. If viewed in daylight, its color is greenish blue to dark yellow-green. If viewed in incandescent or candle light, its color is pink to red. This is called the “Alexandrite effect”. Alexandrite effect is the phenomenon of an observed color change from greenish to reddish with a change in source illumination. Alexandrite results from small scale replacement of aluminium by chromium ions in the crystal structure, which causes intense absorption of light over a narrow range of wavelengths in the yellow region (580 nm) of the visible light spectrum. Because human vision is more sensitive to light in the green spectrum and the red spectrum, alexandrite appears greenish in daylight where a full spectrum of visible light is present and reddish in incandescent light which emits less green and blue spectrum.This color change is independent of any change of hue with viewing direction through the crystal that would arise from pleochroism. |
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