Chrysoberyl is a hard and durable gem with a various forms and colors from red, green, yellow, orange ,brown, pink, gray, black or multicolor.
Best known varieties are Alexandrite and Cat's eye.
Alexandrite is the rarest form and very expensive and has a different colors in natural and artificial light.
Despite the name, chrysoberyl and beryl are very different gemstone but both contain beryllium.
Chrysoberyl is a very hard material with a 8,5 on the Mohs scale, between corundum and topaz.
Characteristics:
Chemical Formula: BeAl2O4
Beryllium 7,10%; Aluminum 42,50%; Oxygen 50,40%
19,70% BeO; 80,30% Al2O3
Color: green, yellow, brown, green, red under incandescent light, pale green, yellow, red in daylight
Crystal habit tabular prismatic, prominetly striated
Hardness: 8,5 Mohs
Crystal system orthohombic - dipyramidal
Refractive index 1,744 - 17,55
Fracture: conchoidal to uneven
Streak white
Luster vitreous
Specific gravity: 3,5-3,84
Density 3,5 - 3,84; average 3,67
Optical properties: biaxial (+)
Transparent to translucent
Pleochroism: X = red; Y = yellow orange; Z = emerald green
Special characteristics:
Alexandrite - color change from green to red
Cmophane - chatoyant
Non-fluorescent
Tests: 8,5 Mohs, streak white; eye's cat effect, alexandrite effect; yellow color
Varieties:
Alexandrite - variety of chrysoberyl that changes color depending on the light source, from artificial light (tungsten/halogen) and daylight.
The color change from red to green is due to strong absorption of light in a narrow yellow portion of the spectrum while allowing large bands of more blue-green and red wavelengths to be transmitted.
alexandrite effect is also its name
Alexandrite results from small scale replacement of aluminium by chromium ions
Because human vision is most sensitive to green light and least sensitive to red, alexandrite appears greenish in daylight where the full spectrum is visible and reddish in incandescent light which emits less green and blue spectrum.
Cymophane is also named cat's eye with chatoyancy or opalescence, well seen when cut to carbochon form
Cymophane is translucent yellowish chatoyant chrysoberyl called also cat's eye.
Other minerals can have cat's eye effect like tourmaline, scapolite, corundum, spinel and quartz being similar in appearance
Also can have reflections known as cymophane effect like moon stone
Cat's eye - variety that shows cat's eye effect when polished carbochon.
Similar stones: topaz, heliodor, peridot, yellow sapphire, citrine, zircon - all can look like chrysoberyl
Cat's eye chrysoberyl can be distinguished byt its hardness of 8,5 Mohs
Can have a very weak fluorescence of red in long wave and red or greenish yellow in short wave.
Most common activator is Cr and other are V
Cr replacing Al with peak of 678, 680 nm
TiO 540 nm
V 720 nm, 689, 698, 703 nm
Other names Chrysolite alexandrit alexandritul ochiul pisicii ochi pisica cat eye cats eye cat s eye crisoberil crisoberilul chrysoberil
Best known varieties are Alexandrite and Cat's eye.
Alexandrite is the rarest form and very expensive and has a different colors in natural and artificial light.
Despite the name, chrysoberyl and beryl are very different gemstone but both contain beryllium.
Chrysoberyl is a very hard material with a 8,5 on the Mohs scale, between corundum and topaz.
Characteristics:
Chemical Formula: BeAl2O4
Beryllium 7,10%; Aluminum 42,50%; Oxygen 50,40%
19,70% BeO; 80,30% Al2O3
Color: green, yellow, brown, green, red under incandescent light, pale green, yellow, red in daylight
Crystal habit tabular prismatic, prominetly striated
Hardness: 8,5 Mohs
Crystal system orthohombic - dipyramidal
Refractive index 1,744 - 17,55
Fracture: conchoidal to uneven
Streak white
Luster vitreous
Specific gravity: 3,5-3,84
Density 3,5 - 3,84; average 3,67
Optical properties: biaxial (+)
Transparent to translucent
Pleochroism: X = red; Y = yellow orange; Z = emerald green
Special characteristics:
Alexandrite - color change from green to red
Cmophane - chatoyant
Non-fluorescent
Tests: 8,5 Mohs, streak white; eye's cat effect, alexandrite effect; yellow color
Varieties:
Alexandrite - variety of chrysoberyl that changes color depending on the light source, from artificial light (tungsten/halogen) and daylight.
The color change from red to green is due to strong absorption of light in a narrow yellow portion of the spectrum while allowing large bands of more blue-green and red wavelengths to be transmitted.
alexandrite effect is also its name
Alexandrite results from small scale replacement of aluminium by chromium ions
Because human vision is most sensitive to green light and least sensitive to red, alexandrite appears greenish in daylight where the full spectrum is visible and reddish in incandescent light which emits less green and blue spectrum.
Cymophane is also named cat's eye with chatoyancy or opalescence, well seen when cut to carbochon form
Cymophane is translucent yellowish chatoyant chrysoberyl called also cat's eye.
Other minerals can have cat's eye effect like tourmaline, scapolite, corundum, spinel and quartz being similar in appearance
Also can have reflections known as cymophane effect like moon stone
Cat's eye - variety that shows cat's eye effect when polished carbochon.
Similar stones: topaz, heliodor, peridot, yellow sapphire, citrine, zircon - all can look like chrysoberyl
Cat's eye chrysoberyl can be distinguished byt its hardness of 8,5 Mohs
Can have a very weak fluorescence of red in long wave and red or greenish yellow in short wave.
Most common activator is Cr and other are V
Cr replacing Al with peak of 678, 680 nm
TiO 540 nm
V 720 nm, 689, 698, 703 nm
Other names Chrysolite alexandrit alexandritul ochiul pisicii ochi pisica cat eye cats eye cat s eye crisoberil crisoberilul chrysoberil
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