Moissanite vs CZ
At first glance Moissanite resembles diamond and might be mistaken for a diamond, a synthetic (lab grown) diamond or diamond simulant (CZ). When compared with cubic zirconia or CZ (perhaps the world's most popular diamond simulant), the differences are obvious. CZ is an inexpensive simulated diamond look-alike, inferior in almost every gemological property to Moissanite. CZ is mass produced under a myriad of trade names and promoted with various brand names. Please refer to the next section: Commonly Marketed Gemstones & Diamond Alternatives.
CZ is too soft
Hardness is the resistance of a gemstone to being scratched or the facets being worn down. Compared to Moissanite, CZ has less than one half (45%) the hardness of Moissanite as measured using the Knoop indention test: 1370 kg/mm2 vs. 3000 kg/mm2. Therefore, Moissanite is 219% harder. Because CZ scratches easily, it can lose its surface luster after just a few months or years with regular wear.
CZ is not tough enough
Toughness is the resistance to chipping and breaking. Compared to Moissanite, CZ has only 1/3 the toughness: 2.4 PSI compared to 7.6 PSI. Therefore Moissanite is over 300% more resistant to chipping.
CZ has inferior optical properties
The beauty and sparkle of engagement gemstones is found in their brilliance, fire and luster.
Optical Anamolies: Windowing
The lower refractive index of CZ causes the stone to exhibit substantially more "windowing" than a Moissanite or diamond and gives CZ what many women refer to as a "glassy" appearance.
CZ strong affinity to dirt
CZ has a very strong affinity to dirt. Another reason many consumers feel that CZ quickly loses its luster and "looks cloudy" is because hand oils, cosmetics, etc. will quickly cling to the gemstone. Given the inferior refractive index of a CZ compared to a diamond or Moissanite, even a little bit of dirt can make the CZ appear dull or lifeless. This in turn requires the wearer to have to clean it often, we have had customers tell us even multiple times a day, to keep it sparkling. Although Moissanite can get dirty with time, it is much more resistant to dirt than CZ and even a diamond, which means it will stay cleaner longer.
CZ lacks stability and durability
CZ is sensitive to heat. When exposed to too much heat, CZ stones will shatter and turn a very opaque, milky color. This can be a problem if you would like to make modifications to your CZ jewelry such as ring sizing. Many jewelers will refuse to perform repairs on CZ jewelry.
In the end, CZ is great for cheap fashion jewelry, but is simply too soft for jewelry if you intend to wear it frequently (i.e. bridal jewelry), it has too strong an affinity to dirt, and its optical properties (luster, fire and brilliance) all fall short when compared to a Moissanite. Unlike Moissanite and diamond, CZ will not stand the test of time.