Cubic zirconia is a beautiful and inexpensive alternative to diamonds, but for many people, nothing can replace the romance and allure of a large, sparkling, fully appraised and insured diamond ring. Even if you do not feel this strongly about diamonds, you still should double check the value of a ring or other piece of jewelry before making a purchase, especially if the price seems too good to be true. While ideally you should take your potential purchase to a licensed gemologist, if you do not have that luxury then at least look for these telltale signs of cubic zirconia before you end up paying big money for a stone worth less than $100.
Look for rounded corners. No stone, grown or natural, can hold the sharp angles that a diamond can. If the angles of the facets on the edge of your stone are rounded rather than distinct and pointed, then you likely have a cubic zirconia on your hands.
Note the lack of inclusions. Cubic zirconia are naturally flawless, whereas very few diamonds in the world have no inclusions. In fact, many jewelry owners use the unique inclusions in their diamonds to identify the stone because no two diamonds have the same flaw. If you cannot see any inclusions even with a microscope, you should not purchase the stone without first checking with a gemologist.
Suspect specimens with unusually brilliant "fire." Cubic zirconia refracts more light than natural diamonds, making its surfaces brighter and giving it a rainbow effect. In diamonds, this brilliance is called "fire," but if a diamond seems unnaturally bright you may want to give it a second look, as most diamonds have only limited brilliance.
Expose the gem to the sun. Cubic zirconia develops a slight gray cast to the stone if it is exposed to the sun for an extended period of time.
Compare the carat weight of the gem to a diamond of equal carat value. Cubic zirconias weigh slightly more than diamonds of equal size. If your stone appears to weight "heavy" compared to a confirmed diamond of comparable size, then you should consult a licensed gemologist or jewelry appraiser before buying.