Last updated on February 24, 2021
It is a popular misconception that lab-grown diamonds and cubic zirconia are the same stones. Although they can look similar to an untrained eye, these two have a completely different chemical composition and physical properties. Let’s go into details and find out how to tell the difference between lab-grown diamonds and cubic zirconia.
Lab-Grown Diamonds vs Cubic Zirconia Composition
Lab-grown diamonds, also known as synthetic, man-made, cultured or cultivated diamonds, have the same crystal structure and chemical composition (100% carbon) as natural/mined diamonds.
Synthetic diamonds also have the same physical and optical properties as the natural stones, meaning they have the same hardness (10 on the Mohs scale) and refractive index (2.417 – 2.419). The only difference between lab-grown and natural diamonds is that lab-grown diamonds are created synthetically in laboratories, while natural ones are mined from the earth.
Cubic zirconia is also a synthetically created stone, but its crystal structure and chemical composition are completely different. While lab-grown diamonds consist of carbon, cubic zirconia, also known as CZ, is the cubic crystalline form of zirconium dioxide and contains zero carbon. CZ is not a diamond, but it is one of the most popular gems used as a diamond simulant due to its affordable price.
Lab-Grown Diamonds vs Cubic Zirconia Colour, Clarity and Cut
The colour of lab-grown diamonds is graded on a scale from D to Z, where D signifies a completely colourless stone and Z means an easily noticeable yellow or brown tint.
While most synthetic diamonds are between F and J on the colour scale, cubic zirconia is purely colourless and displays colourful flashes of light similar to moissanite.
Although the clarity of lab-grown diamonds is graded on FL to I3 clarity scale developed by GIA, HPHT synthetic diamonds often contain metal inclusions such as iron, nickel and cobalt, while CVD diamonds often come with graphite or other mineral inclusions.
Cubic zirconia usually comes internally flawless, which makes it very attractive to buyers around the world. However, this is also one of the main ways to tell CZ and diamond apart as no diamond is perfect.
In terms of cut quality, there is no difference between lab-created and natural diamonds. The precision of angles, proportions and symmetry are the factors that determine a diamond’s cut quality which is graded on the scale of Excellent, Very Good, Good, Fair and Poor.
The cut quality of cubic zirconia is graded through the A rating system which only applies to mass-produced machine cut stones. Rated from A or 1A to AAAAA or 5A, 1A is considered the lowest quality of machine-cut CZ while 5A is the best possible quality.
Lab-Grown Diamonds vs Cubic Zirconia Durability and Weight
Since lab-grown diamonds and cubic zirconia have different chemical composition, they differ in physical properties, one of which is their hardness and durability as a result.
Diamonds, including lab-grown stones, are the hardest gemstones with the score of 10 on the Mohs scale. The hardness of cubic zirconia is 8.25 – 8.50, meaning it is less durable, easier to scratch and break than cultivated diamonds.
Since cubic zirconia is softer than man-made diamonds, these two stones also differ in how sharp the edges of their facets are when cut and polished. Lab-grown diamonds, like natural ones, have very sharp facet edges, while cubic zirconia has more rounded edges which become even more rounded with time, making the stone look foggy.
The density of cubic zirconia is about 1.7 times that of a diamond, meaning if you compare a CZ with a lab-grown diamond of the same size, the first will be significantly heavier.
Lab-Grown Diamonds vs Cubic Zirconia Sparkle and Price
Another significant difference between cubic zirconia and synthetic diamonds is their refractive indices. This optical property defines the level of fire, brilliance and scintillation a gemstone exhibits.
Cubic zirconia has a much lower refractive index (2.17) than a diamond (2.42). That means when cut and polished, it does not show true brilliance and fire because light passes through CZ much differently.
It has higher dispersion (0.058-0.066) than a diamond (0.044), and for this reason, when exposed to light, CZ exhibits flashes that are more colourful than those of cultivated diamonds.
Although lab-grown diamonds cost up to 40% less than natural ones due to their shorter supply chain, they are still significantly expensive compared to cubic zirconia.
CZ costs a fraction of the price of a lab-grown diamond of the same carat weight, colour and clarity. In other words, cubic zirconia carries very little market value, making them a good alternative for those tight on budget.