Alexandrite Gemstone and Basic Information in 90 minutes with Changing Color - Alexandrite Effect

Alexandrite is a variety of Chrysoberyl, a beryllium aluminum oxide with a hardness of 8.5. Its crystal pattern is orthorhombic, and it sometimes forms in hexagonal-looking twinned crystals. The magic of gem quality Alexandrite is in its property of color change; it is ruby alike red in incandescent light and emerald alike green in daylight as per perfect color changing variation aka Alexandrite effect.

Chrysoberyl is semi-precious gem, and not uncommon. However, Alexandrite is considered as precious gem due to its magical color changing effect, and one of the most rare and most expensive gems in the world. Alexandrite was discovered in the Ural Mountains in 1830, and was named after the Russian ruler Alexander II, on whose birthday it was supposedly found.

Changing colors:
The alexandrite variety of Chrysoberyl displays a color change, from greenish to reddish, when seen in different light conditions. Alexandrite appears greenish in daylight, where a full spectrum of light is present, but reddish in incandescent light, because it contains less of the green and blue spectrum. The color change is due to chromium atoms replacing the aluminum in the Chrysoberyl structure.

Basic Information:
Mineral class: Oxides
Mineral species: Chrysoberyl
Crystal system: orthorhombic
Chemical composition: BeAl2O4
Variety: alexandrite and cat's-eye alexandrite (very rare)
Trade names: alexandrite and cat's-eye alexandrite (very rare)
Color: daylight or fluorescent light: bluish green, yellowish green, brownish green or grayish green incandescent light: orangish red, brownish red or purplish red
Transparency: transparent
Luster: from vitreous to sub adamantine
Optical phenomena: color change, there may also be chatoyancy
Refractive Indices: 1.746 - 1.755 (+ .004, - .006)
Optic character: biaxial positive, DR
Birefringence: from .008 to .010
Dispersion: .015
Pleochroism: strong - green, orange and violacious red
Fluorescence: from inert to moderate - red (UVC and UVL)
Absorption spectrum: two strong lines at 680.5 and 678.5 nm and weak lines at 665, 655 and 645 nm, partial absorption between 580 and 630 nm, three weak lines at 476.5, 473 and 468 nm and generalized absorption of the violet region
Specific gravity: 3.73 (± .02)
Fracture: Conchoidal with vitreous to greasy luster
Cleavage: none
Identifying characteristics: fingerprints, silk, color change
Possible treatments: fracture filling with oil or resin
Hardness: 8.5
Reaction to heat: stable
Stability to light: stable
Reaction to chemicals: none
Possibly mistaken with Andalusite, color change garnet, natural and synthetic corundum, natural and synthetic spinel and synthetic alexandrite

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