Phenomenal gemstones are gems that exhibit special optical characteristics, or “phenomena”. The unusual optical effects are usually identified by moving a strong concentrated light over a gemstone. Because of this, you will often see a special effect when light interacts with a gem.
Cat’s Eye Effect
A gemstone with cat’s eye effect, or chatoyancy, will display a single sharp bright line. The line is caused by fine, fibrous inclusions within the gem. The line mimics the characteristic slit that runs through the center of a cat’s eye so it picked up the well-known “cat’s eye” designation.
It’s important to note that “cat’s eye” always refers to chrysoberyl and other gems exhibiting the effect need to be designated, like cat’s eye ruby.
Star Stones
The star effect or asterism that can be found in a select few gems and is a well-known gem phenomena. Long needle shaped inclusions intersect in the gem to form a star if the gem is fashioned a specific way.
Star Sapphire and Star Ruby are both fine specimens of asterism with their bold colors providing a deep contrast for the bright light of the star. Stones with stars that are sharp and centered are far more valuable than a weaker star.
Color Change Gemstones
One of the rarest gem phenomena is color change. Gems like Alexandrite will change colors when exposed to daylight and then incandescent light. The most valuable stones change from a blue to a reddish color.
Although color change is an exciting phenomena, it is extremely rare. Exotic color change stones can get costly but there are less expensive alternatives like color-change garnet.
Find Unique Treasures at Hart Gem Shows Events
Hart Gem Shows holds giant gem show events for natural earth enthusiasts to come together and share their love of the natural world. The Denver Gem Show comes to the National Western Complex from September 11 – 20, 2026 and the Fall New Jersey Gem Show is happening at the NJ Convention & Expo Center in Edison, NJ from September 30 – October 4, 2026. Don’t miss your chance to explore minerals, gems, jewelry, and more at two of the biggest gem shows of the year!