Last updated on June 21, 2021
Although diamond and cubic zirconia can appear similar to an untrained eye, these two gemstones have different chemical compositions and physical properties. In this guide, you will learn how to spot the difference between diamond vs cubic zirconia.
Diamond vs Cubic Zirconia Composition
Diamonds can be both natural and synthetic. They have the same crystal structure and chemical composition, which is 100% carbon. Cubic zirconia, also known as CZ, is a synthetic stone created in laboratories. CZ is the cubic crystalline form of zirconium dioxide, and it contains zero carbon.
Due to their different composition and crystal structure, cubic zirconia and diamond have different density or specific gravity. CZ has a density of 5.65 – 5.95, while diamond has a density of 3.52 ±0.01, meaning cubic zirconia is a denser gemstone, making it heavier than diamond. In other words, a CZ and a diamond of the same carat weight will not be of the same size. The cubic zirconia will be slightly smaller than the diamond.
Diamond vs Cubic Zirconia Durability
Since diamond and cubic zirconia have different chemical composition, they differ in physical properties, one of which is their hardness and durability as a result.
Diamond is the hardest gemstone, with a 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 diamonds.
These two stones also differ in how sharp the edges of their facets are when cut and polished. Since CZ is not as hard as diamond, it can not be cut and faceted to match a real diamond. Both lab-grown and natural diamonds have very sharp facet edges, while cubic zirconia has more rounded edges, which become even more rounded with time, making the stone look foggy and dull.
Diamond vs Cubic Zirconia Colour, Clarity and Cut
Diamond colour 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.
Since cubic zirconia is a lab-created stone where manufacturers can control the growth process, the final product usually comes purely colourless and displays colourful flashes of light similar to moissanite.
Diamond clarity is graded on FL to I3 clarity scale developed by GIA. The majority of diamonds found in nature contain lots of inclusions, and it is hard to find a stone with only a couple of visible flaws. HPHT synthetic diamonds often contain metal inclusions such as iron, nickel and cobalt, while CVD diamonds come with graphite or other mineral inclusions. Cubic zirconia, on the other hand, 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 mined 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.
Diamond vs Cubic Zirconia Sparkle and Value
Another significant difference between diamond and cubic zirconia 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 (2.171 – 2.177) than a diamond (2.417 – 2.419), meaning when cut and polished, it does not show true brilliance and fire because light passes through CZ much differently.
CZ 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 diamonds.
The price per carat is very different between diamond and cubic zirconia. Mined diamonds are very expensive. Lab-grown diamonds cost up to 40% less than natural ones due to their shorter supply chain, but they are still significantly expensive compared to cubic zirconia.
CZ costs a fraction of the price of a diamond of the same carat weight, colour and clarity. In other words, cubic zirconia carries very little market value, making it a good alternative for those tight on budget.