Moissanite has a property known as double refraction. Double refraction is when a ray of light passes through the gemstone, is slowed, bent, and split in two. Sapphire is a double refractive material as well, as are peridot, tourmaline, and zircon. To some degree, it is this property that gives Moissanite its amazing fire. However, it is often cited by critics of Moissanite, typically by companies who sell CZ, as a disadvantage, claiming that the double refraction will make the stone appear blurry. What they don't say is that every double refractive gem has at least one direction in which the material behaves like a singly refractive gem. This is referred to as the optic axis and does not break light into two rays.
Moissanite is cut so that this direction of single refraction is through the table. This means that the doubling is not apparent when the stone is viewed through the table (top of the stone). Moissanite must be viewed at 10x magnification (jewelers loupe) through any other crown facet (e.g. star, or bezel) to see the doubling. Most of our customers do not know or realize that Moissanite is double refractive, and we provide this explanation and images to explain that, although it is a unique property of Moissanite, it does not negatively affect its beauty.
Below is a video of our new emerald cut Charles & Colvard created Moissanite. We feel it is very illustrative when explaining Moissanite's double refractive properties. If the doubling were easily seen in a brilliant cut stone (and it is not, as explained above), it would be even more readily apparent in a step cut such as an emerald cut given its long straight lines. However, based on the picture below you can see that it is not.