Change of Color
Color change garnet
is one of the most rare, interesting, and phenomenal of all gemstones
. The color change can be intense and equal to the color change of top quality alexandrite and fine color change garnets can easily be mistaken for alexandrite. Some of the best stones are from the deposit in Bekily, Southern Madagascar. Stones from this mine are well known for their strong alexandrite like color change.
Change of color is not the same as the changes in color with crystal orientation that affects tourmaline and iolite, which are due to the optical property called pleochroism. Only rare tourmalines, garnets and alexandrite absorb certain wavelengths of light so strongly that in sunlight and indoor light they appear different colors.
"Chatoyance" is French for cat's-eye. When impurity minerals occur in fibers, they give gemstones
a silky appearance. When the fibers line up along one of the crystalline axes, a stone can be cut to display a bright reflective line—a special effect called cat's-eye.
Pictured cat's eye chrysoberyl is also known as cymophane
. The name being derived from the Greek words cyma and phanes, meaning “wave” and “appearance.” Microscopic needle-like inclusions inside the stone reflect a streak of light known as the cat’s eye.
The cat's eye’s inclusions are aligned parallel to the crystallographic axis and they are always cut as cabochons with the fibrous need-like inclusions running across the narrow part of the stone as this is the only way to display the effect properly.