Chrysoberyls Gemstone

Color

Standard color light to medium yellow to yellowish green, greyish green, brown to yellow-brown to light blueish yellow to greenish but several other types have color effects:

Color change effect in Alexandrite is primarily red to green, depending on whether it is viewed in lamplight or daylight. These two colors were coincidentally the royal colors of the Russian Czars, hence its popularity in old Russia

Cat's eye Chrysoberyl is yellow to yellowish green; greyish green; brown to brownish yellow

Clarity

Non-phenomenal chrysoberyl is transparent to semi-transparent, comprising a range of colours.
The alexandrite variety contains gems that vary from transparent to semi transparent, and whose colour appears different depending on the light it is viewed in.
Cat's eye chrysoberyl is opaque to semi-transparent, containing minute parallel inclusions that cause chatoyancy.

Cut

Normal Chrysoberyls and alexandrites occur in a variety of standard cuts
Cat's eye chrysoberyl occurs in cabochon due to the nature of the effect (chatoyancy)

Treatment

No known treatments in significant numbers
One case known of brown cat's eye chrysoberyls in the 1990's which was irradiated in a nuclear facility to deepen the brown colors

Care

With excellent hardness and toughness, chrysoberyls of all types are extremely resilient for use in jewelry and may be worn under daily conditions.
Alexandrites and cat's eye chrysoberyls are quite rare to begin with and as such highly collectible due to their exotic, phenomenal qualities. A premium is placed on gems that contain strong colour change qualities, since with alexandrites a predominantly "muddy" mix of greens, browns and reds tends to be the norm, resulting in a vague colour change.
With cat's eyes, a strong, sharp and unwavering silvery line that is visible from girdle-to-girdle is highly desirable, accompanied by rich green, yellow or brown colours.