chrysoberyl

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Photo courtesy of Vettri Gems

Species:  Chrysoberyl
Mohs Hardness:  8.5 out of 10
Color:  Non-phenomenal chrysoberyl occurs in various colors, but is commonly yellow to yellowish green, bluish green, brownish green.  May show phenomena such as cat's eye or color change
RI:  1.746 to 1.755 (+0.004 / -0.006)
Birefringence:  0.008 to 0.010
SR/DR/AGG:  DR
Clarity Type:  Type I
Optic Character:  Biaxial positive
Pleochroism:  Depends on variety
Spectrum:  Not diagnostic
Fluorescence:  Depends on variety
SG:  3.73 (+/- 0.02)

chrysoberyl facts

Chrysoberyl is usually found in various shades of yellow, though some are brown, green, or orange.

Several varieties of chrysoberyl are phenomenal, such as cat's eye chrysoberyl and alexandrite.

phenomenal chrysoberyl

alexandrite

Natural alexandrite in daylight vs incandescent light [Photo by Scott Papper, GIA GG, AJP, CMA (NAJA)]

Alexandrite possesses a rare phenomena known as color change.

Alexandrite appears green in sunlight and red/purple in lamplight.  "Emerald by day, ruby by night."

Natural alexandrite is very rare.  It was originally discovered in Russia's Ural Mountains in the 1830s.  It's now found in Sri Lanka, East Africa and Brazil.

cat's eye

Photo courtesy of JTV

Cat's eye chrysoberyl possesses a rare phenomena known as chatoyancy.

Cat's eye occurs in many different colors and is identified by its narrow slit that resembles a feline's pupils.

The cat's eye effect is due to many parallel, fibrous needle inclusions that scatter and reflect light back in a thin band.

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All photos courtesy of Scott Papper, GIA GG, AJP, CMA (NAJA)