Quick answer: Moissanite and diamond look very similar once set in a ring, but they are different gemstones. Diamond is harder (10 on the Mohs scale against moissanite's 9.25) and has a crisp white sparkle. Moissanite shows more rainbow "fire" and usually costs far less, especially above 1 carat. If you want the classic, most durable stone, choose a diamond (natural or lab-grown). If you want a large, brilliant stone on a tighter budget, moissanite is an excellent, durable choice for everyday wear.
Choosing between moissanite and diamond is one of the most common questions we hear from couples across the UK. Both are beautiful, both are durable enough for an engagement ring, and both can be set in solid gold. The right choice depends on what matters most to you: tradition, sparkle, size or budget. This guide explains the real differences so you can decide with confidence.
Moissanite vs diamond at a glance
| Feature | Diamond | Moissanite |
|---|---|---|
| What it is | Pure carbon (natural or lab-grown) | Silicon carbide (lab-created) |
| Hardness (Mohs scale) | 10 – the hardest natural material | 9.25 – harder than sapphire and ruby |
| Refractive index (brilliance) | 2.42 | 2.65–2.69 |
| Dispersion (fire) | 0.044 | 0.104 – about twice diamond's rainbow flashes |
| Look | Crisp white sparkle | Stronger rainbow sparkle, especially in sunlight |
| Colour | Graded D (colourless) to Z | Colourless or near-colourless; larger stones can show a slight warm or grey tint in some lighting |
| Grading / certification | GIA for natural diamonds, IGI for lab-grown diamonds | GRA certificate |
| Typical price | Highest (natural) or mid-range (lab-grown) | Lowest of the three, and the gap grows with carat size |
What is moissanite?
Moissanite is a gemstone made of silicon carbide. It was first identified in 1893 by French scientist Henri Moissan in fragments of a meteorite, which is where its name comes from. Natural moissanite is extremely rare, so every moissanite used in jewellery today is created in a laboratory. It is not a "fake diamond" or a diamond simulant like cubic zirconia; it is a genuine gemstone in its own right, with its own optical properties.
What is a diamond?
A diamond is pure carbon arranged in a crystal structure, which makes it the hardest natural material on Earth. Natural diamonds form deep underground over billions of years. Lab-grown diamonds are chemically, physically and optically identical to natural diamonds; they are simply grown above ground in weeks rather than mined. Both are real diamonds.
Sparkle: which one shines more?
This is where the two stones differ most. Moissanite has a higher refractive index (2.65–2.69 against diamond's 2.42) and more than double the dispersion (0.104 against 0.044). In everyday terms:
- Diamond gives a balanced mix of white light (brilliance) and flashes of colour (fire). It looks crisp and bright.
- Moissanite throws noticeably more rainbow-coloured flashes, particularly in direct sunlight. Some people love this extra fire; others prefer diamond's cooler, whiter sparkle.
Neither is "better". It is a matter of taste. If you can, compare them side by side in natural daylight and indoor lighting before you decide.
Durability: can moissanite be worn every day?
Yes. At 9.25 on the Mohs hardness scale, moissanite is one of the hardest gemstones used in jewellery, harder than sapphire and ruby (both 9). It resists scratches and chipping well and will keep its sparkle for a lifetime with normal care. Diamond, at 10, is harder still, which is why it remains the benchmark for rings worn every day for decades. For an engagement ring, both stones are durable enough for daily wear.
Colour and clarity
Diamonds are graded on the D-to-Z colour scale, with D being completely colourless. Modern moissanite is sold as colourless or near-colourless, and in smaller sizes it looks icy white. In larger stones (roughly 2 carats and above), moissanite can sometimes show a faint warm or grey tint under certain lighting, such as fluorescent office lights. Choosing a colourless grade and a white-gold setting helps keep the stone looking bright white.
Price: how much can you save?
Price is the main reason many couples choose moissanite. Moissanite costs a fraction of a natural diamond and is usually well below a lab-grown diamond of the same size. The saving grows as the stone gets bigger: at 1 carat, moissanite typically costs noticeably less than a lab-grown diamond, and at 2–3 carats the difference often becomes more than half.
That means moissanite lets you choose a bigger centre stone, a more elaborate setting, or 18ct gold instead of 14ct for the same budget. Lab-grown diamond prices have also fallen sharply in recent years, so if you would like a real diamond, a lab-grown stone is now far more affordable than a natural one.
Can you tell the difference?
To the naked eye, most people cannot tell a well-cut moissanite from a diamond once it is set in a ring. The biggest giveaway is moissanite's stronger rainbow fire in bright light. Jewellers use a dedicated moissanite tester to tell them apart, because a standard diamond tester can register moissanite as diamond due to their similar heat conductivity. Under magnification, moissanite also shows "double refraction", making the facet edges look slightly doubled.
Ethics and sustainability
Moissanite and lab-grown diamonds are both created in a laboratory, so neither involves mining. That makes them popular choices for couples who want a conflict-free stone with a smaller environmental footprint. If you prefer a natural diamond, ask for a GIA grading report to confirm the stone's quality.
Moissanite or diamond: which should you choose?
Choose moissanite if you:
- want the biggest, most brilliant stone for your budget
- love extra rainbow sparkle
- prefer a lab-created, mining-free gemstone
- would rather spend more on the setting, the gold or the wedding itself
Choose a diamond if you:
- want the traditional engagement stone with the highest hardness
- prefer a crisp, white sparkle
- value the recognition and resale market that diamonds carry
- are happy to choose lab-grown to get a real diamond at a lower price
Shop moissanite and diamond rings at The Karat Store
Our engagement rings are handcrafted to order in solid 10ct, 14ct or 18ct gold, in yellow, white or rose gold. Our stones come with independent certification: GRA for moissanite, IGI for lab-grown diamonds and GIA for natural diamonds. Every order comes with free, insured delivery and our 60-day free returns.
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- Lab-grown diamond engagement rings
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Not sure which stone is right for you? Message us on WhatsApp and we'll help you compare.
Frequently asked questions
Is moissanite a real gemstone?
Yes. Moissanite is a genuine gemstone made of silicon carbide. It is not a diamond and not a simulant like cubic zirconia; it has its own distinct physical and optical properties.
Does moissanite get cloudy over time?
No. Moissanite does not go cloudy or change colour. Like any gemstone, it can look dull when covered in everyday oils and lotions, and a simple clean with warm soapy water and a soft brush restores its sparkle.
Is moissanite harder than diamond?
No. Diamond is 10 on the Mohs scale and moissanite is 9.25. Moissanite is still harder than almost every other gemstone, including sapphire and ruby, so it is very suitable for everyday wear.
Does moissanite sparkle more than diamond?
Moissanite has more fire (rainbow sparkle) than diamond because its dispersion is more than twice as high. Diamond has a whiter, crisper sparkle. Which looks better is personal preference.
Will a diamond tester detect moissanite?
A basic thermal diamond tester may read moissanite as diamond because the two conduct heat similarly. Jewellers use a dedicated moissanite tester or magnification to tell them apart.
Is moissanite cheaper than a lab-grown diamond?
Usually, yes. Moissanite is typically less expensive than a lab-grown diamond of the same size, and the price difference increases with carat weight.
Is moissanite a good choice for an engagement ring?
Yes. Moissanite is durable, brilliant and affordable, which makes it a popular engagement ring choice in the UK. Set in solid gold, it will last a lifetime with normal care.