When is a diamond not a real diamond? When it’s a diamond simulant! These pretenders do their best to imitate the look of a diamond but are much less valuable. Some do a much better job of simulating a diamond. Here’s what you need to know about the most common diamond imitations.
Crystal
The first diamond simulant is glass: what we generally call lead crystal. When hard glass that could be cut was first developed, it wasn’t long before people began cutting it into gem shapes. Cut glass crystal is very inexpensive but unfortunately it isn’t a very good diamond simulant. Even lead crystal has a relatively low refractive index, which means that light goes right through it instead of being reflected back as brilliance. As a result crystal cut into gem shapes has much less brilliance and sparkle than diamond.
To make crystal glass a better diamond imitation in antique jewelry, goldsmiths often put thin foil behind the gem or mirrored the back to make the glass reflect better. These were the first “rhinestones.” Today crystal is only used to imitate diamond when cost is the main factor. Softball size imitation diamond paperweights are usually made out of crystal. Swarovski has now developed crystal that is lead-free: the lead that makes the glass hard and more brilliant has been replaced with other elements for environmental reasons.
White Sapphire
For centuries, the best diamond simulant was colorless sapphire. This gem is durable, brilliant, and can be faceted just like diamond. But because it is also a rare natural gem in its own right, it isn’t as affordable or available as other diamond simulants. In the 1920s, synthetic sapphire was invented, making colorless sapphire much more affordable and available. In fact, today it’s used instead of glass for watch crystals and supermarket scanners because it is much more durable. White sapphire is still used as a diamond substitute today in inexpensive birthstone jewelry and class rings.
Strontium Titanate, YAG & GGG
Strontium titanate is a man-made diamond simulant invented in the early 1950s. It’s brilliant and has much more rainbow fire than diamond, which made it popular as a diamond imitation in the decades that foilowed. Retailers sold strontium titanite as "Fabulite," "Diagem," and other creative names. Unfortunately strontium titanate only has a hardness of 5.5, which is softer than most gems used in jewelry and much softer than diamond. It chips and scratches easily when worn in rings.
Starting in the 1970s, new man-made diamond simulants such as YAG (yttrium aluminium garnet) and GGG (gadolinium gallium garnet) quickly took market share away from strontium titanate. These diamond simulants looked more like diamond and were more durable than strontium titanate. All three diamond simulants fell out of favor when cubic zirconia came on the market and are generally only seen in vintage jewelry.
Cubic Zirconia
The most popular diamond simulant is cubic zirconia, popularly known as CZ. Cubic zirconia is a synthetic material grown in the lab specifically as a diamond simulant. Why has it become so popular? It is white, bright, brilliant with a high refractive index, and quite affordable. CZ has a pretty good hardness of 8.5 and is a pretty convincing diamond imitation. It’s more dense than diamond which causes some confusion. A one-carat CZ will be much smaller than a one-carat diamond. That’s why CZ is generally sold by size instead of by carat weight.
Unfortunately some retailers of cubic zirconia, including Diamond Nexus, try to obscure the fact that they are selling a diamond simulant. They use language that suggests that their product is set with lab-grown diamond not a diamond imitation. This enables them to charge more than other sellers of cubic zirconia jewelry.
Moissanite
Moissanite is the crystal form of silicon carbide. This diamond simulant was first grown in the lab in 1993. It has a very high hardness of 9.2 so it’s durable. It has a high refractive index. Like strontium titanate before it has very high dispersion, giving it lots of rainbow fire. It’s doubly refractive, which means you can see some doubling of facets. It also is often not quite white: it often has a slight green or brown tint. These three factors combine to make it a not as effective diamond imitation. As a result it is marketed as a lab-grown gemstone without comparing its appearance to diamond. Moissanite is also much more expensive than CZ, making it a less popular diamond simulant overall. Moissanite is lighter than diamond, so a moissanite the same size as a one-carat diamond will weigh 0.88 carats.
What is the Best Diamond Simulant?
If you are looking for a diamond simulant, cubic zirconia offers the best imitation of diamond at the lowest price. If you are not getting a real natural diamond, why pay more for a lab-grown gem that can be manufactured at a high volume and may not hold its value?
How Top Diamond Simulants Compare to Diamond
| Refractive Index | Dispersion | Hardness | |
| Diamond | 2.42 | 0.044 | 10.00 |
| Cubic Zirconia | 2.17 | 0.060 | 8.25 |
| Moissanite | 2.65 - 2.69 | 0.104 | 9.25 |
| White Sapphire | 1.76 - 1.77 | 0.018 | 9.00 |