Moissanite, Cubic Zirconia and Diamonds are all gemstones. They each have a crystalline structure, although each crystal is not physically identical. Diamonds are comprised of carbon, CZ is derived from zirconium oxide, and Moissanite is a naturally occuring silicon carbide (silicon + carbon). All these gemstones are formed under intense heat, in the ground and in the laboratory.

Diamonds and Moissanite occur naturally although Moissanite occurs only in extremely small quantities, and then only in certain meteor craters distributed across the globe. Chatham diamonds are made in the laboratory and have identical characteristics to a kimberlite diamond. In other words, a Chatham diamond is a diamond and not a simulant.

All three are very close optically and only a trained gemologist, often with the need of special equipment, could differentiate a diamond from a CZ or Moissanite gemstone. It is extremely unlikely that the untrained eye could distinguish these gemstones even under mild magnification.

Diamonds are the hardest substance on earth with a Mohs rating of 10, the highest number on the scale. Moissanite is very close in diamonds to hardness with a Mohs rating at 9.25. CZ is also a very hard substance with a Mohs rating of 8.5 - 9.0. All these stones will cut glass. Keep that in mind when somebody you do not know is giving you the 'deal of a lifetime' on a 2 carat diamond ring.

The hardness of a gemstone is the primary determinant of how it can be cut into facets. Hardness is important for cutting gemstone facets as it determines the intricacy and sharpness of the cuts that can be made. For example, Topaz has a Mohs hardness of 8.0 which limits Topaz jewelry to uncomplicated gemstone facets.

A gemstone's fire is its ability to disperse white light into many colors, like a prism. Moissanite is the fire champ by far. Diamond has less fire than CZ. It is somewhat ironic that after centuries of valuing diamonds for their fire that Moissanite and CZ get devalued for exhibiting even greater fire.

Brilliance is a gemstone's ability to capture light. When light hits the stone at a certain angle it actually gets trapped temporarily inside the stone. A diamond or other gemstone displays brilliance as the trapped light reflects upon itself and sparkles deep within the stone.

Again the champ, Moissanite has the most brilliance. On the refractive scale CZ is 2.2, diamond 2.4 and Moissanite 2.7. Crown glass, for example, has a refractive index of 1.5.

Diamonds, Cubic Zirconia, and Moissanite look very much alike. They differ in the physical characteristics that matter most for jewelry only by degrees of hardness, fire, and brilliance. A well cut Cubic Zirconia gemstone in an attractive setting would almost certainly be more appealing to the eye than a mediocre diamond piece.

Price and lore are the most conspicuous differences.