There are three main gem varieties of Chrysoberyl:
The first type is simply faceted transparent Chrysoberyl that is
usually found in yellowish green to green, yellow and shades of
brown. It is a fine gemstone, but is over-shadowed by its two
cousins.
The second variety is the "cat's eye", also known as
cymophane. The effect is caused by microscopic needle-like
inclusions that reflect light into a single dynamic sliver of light
running along the center of the crystal thus making it look like a
living cat's eye! Although other minerals such as
tourmalines,
scapolite, corundum, spinel
and quartz form "cat's eye" stones,
they must be designated as "tourmaline cat's eye", or "ruby cat's
eye" in the jewellery industry. Only chrysoberyl can be referred to
as "cat's eye" with no other designation.
The third and perhaps most interesting is
Alexandrite. This rare and valuable
gemstone has the unique property of changing color depending on the
type of light that hits it. In sunlight, it appears almost emerald
green, while in artificial incandescent light it appears a
violet-red. Some sapphires show similar ability, and synthetic
sapphires are now on the market being sold as "Alexandrites" but at
substantially lower prices than natural Alexandrite.