Mined Diamond vs Lab Grown Diamond vs Moissanite, Compared

Three stones get considered for almost every engagement ring in Australia: a mined diamond, a lab grown diamond, and a moissanite. They are not three grades of the same thing. Two of them are diamond and one is a different mineral with different optics, and the reason people end up confused is that most comparisons are written to push a reader toward whichever one the writer stocks.

So, the disclosure first. I make engagement rings in a Southbank studio in Melbourne. We sell lab grown diamond and moissanite. We do not sell mined diamonds. You should read the mined column below knowing that, and you should weigh my scoring accordingly, which is why I have written out the criteria for every score rather than just handing you a number.

The scored comparison

Scores out of 10. The criteria are stated in each row so you can disagree with me on the reasoning rather than just the result.

	Mined diamond	Lab grown diamond	Moissanite
What it is	Carbon, crystallised in the mantle over 1 to 3 billion years	Carbon, same lattice, grown in a reactor over 2 to 12 weeks	Silicon carbide, a different mineral, grown in a lab
Hardness (Mohs, resistance to scratching)	10	10	9.25, ahead of sapphire at 9
Chip resistance (toughness, not hardness)	8. Diamond has cleavage planes, so a hard knock at the wrong angle can chip it	8. Identical, for the identical reason	9. No cleavage planes, so it takes a knock better than its hardness score suggests
Refractive index	2.42	2.42	2.65, and doubly refractive
Dispersion / fire (coloured flashes)	0.044	0.044	0.104, roughly two and a half times diamond
Brightness score (how alive it looks in ordinary light)	9	9	9, but differently. More rainbow, less white sparkle
Price at a given size	3. Highest by a wide margin, and the gap widens with carat	7. A fraction of mined at the same spec. From AU$1,350 with us	10. Lowest, and the curve stays flat as size increases. From AU$800 with us
Certification	9. GIA, IGI, HRD reports on the 4Cs	9. IGI, GIA, GCAL, same 4Cs, laser inscribed girdle	6. GRC certified. Real, but a smaller framework than diamond grading
Resale	3. Loses most of the retail price. Better than the other two, still poor	2. Poor, and prices in the category keep falling	2. Poor, but there is much less to lose
Availability at 2ct and above	3. Scarce and priced accordingly	9. Ordinary stock	10. Ordinary stock, at a small increment
Sourcing transparency	5. Kimberley Process covers conflict financing only, not labour or environment	7. No mining, but the footprint depends on the reactor's electricity	7. Same electricity caveat, less power per stone
We sell it	No	Yes	Yes

Hardness, and why it is the wrong thing to worry about

Diamond is 10 on the Mohs scale. Moissanite is 9.25. Sapphire is 9. Everything you touch in daily life, including household dust, which is largely quartz at 7, sits below all three. On scratch resistance, all three of these stones are fine forever, and the difference between 10 and 9.25 is not something you will experience.

The number that actually matters is toughness, which Mohs does not measure. Hardness is resistance to scratching. Toughness is resistance to breaking. Diamond, for all its hardness, has cleavage planes: directions along which the crystal will part cleanly if it takes a sharp knock at the right angle. Moissanite does not have them. So the counterintuitive result is that a moissanite is a little harder to chip than a diamond, despite being softer.

In practice, for all three, the setting decides this. A stone with its girdle sitting proud of the claws will meet a doorframe eventually. A bezel, or claws with proper coverage over the girdle, is what protects it. Ask about that before you ask about Mohs numbers.

Refractive index, and why moissanite shows more fire

Two optical numbers explain everything about how these stones look.

Refractive index measures how much the stone bends light. Diamond is 2.42, mined or lab grown, because it is the same material. Moissanite is 2.65. Higher RI means more light is trapped and returned to the eye rather than leaking out the bottom, so a well cut moissanite is very bright.

Dispersion measures how much the stone splits white light into its component colours. Diamond is 0.044. Moissanite is 0.104, roughly two and a half times as much. That is the "fire": the flashes of red, orange and blue you see when the stone moves. Moissanite has visibly more of it.

Whether that is a feature or a problem depends on you. Some people love it and that is precisely why they buy moissanite. Others look at a large moissanite under bright downlights and find the rainbow effect too much, and describe it as looking "disco". Both reactions are common and neither is wrong. The effect is far more noticeable at larger sizes and in bright directional light, and much less so under 1ct or in daylight.

There is one more physical difference worth knowing. Moissanite is doubly refractive: it splits light into two paths, so under magnification, looking through the crown at an angle, you can see facet edges appear doubled. Diamond is singly refractive and does not do this. Nobody sees it with the naked eye at arm's length. It is how a jeweller with a loupe identifies moissanite in about four seconds.

One practical consequence of the material difference: moissanite is less dense than diamond, so a moissanite and a diamond of the same millimetre size do not weigh the same. That is why reputable sellers, including us, quote moissanite by millimetre size or by "diamond equivalent weight" rather than by carat. If a seller lists a moissanite in plain carats, ask them what the actual millimetre diameter is, because that is the number that determines what it looks like on a hand.

Price at 1ct and 2ct equivalents

The shape of the price curve matters more than any single figure.

Diamond, mined or lab grown, is priced per carat, and the price per carat rises as the stone gets bigger. So a 2ct stone is not twice a 1ct stone at the same colour and clarity. It is meaningfully more than twice, and in mined the step up at each round number is steep because large rough is genuinely scarce.

Lab grown diamond has the same shape of curve, because larger stones still take longer to grow and have lower yields, but the whole curve sits far lower. This is why the lab grown advantage is at its most dramatic at 2ct and above: it is the difference between a size being available to a normal budget and not being available at all.

Moissanite has a much flatter curve. The material is manufactured and it is not priced on scarcity, so going up in size costs more, but not dramatically more. If your brief is maximum visible stone for the smallest number, moissanite wins that comparison and it is not close.

Our moissanite designs start at AU$800 and our lab grown diamond designs start at AU$1,350. I am not going to print a 1ct and 2ct price table here, because those numbers move with the metal market and with stone supply, and a stale table is worse than none. The live figures by size sit on the moissanite engagement rings and lab grown diamond engagement rings collections. For mined, I am not going to quote a competitor's price second hand. Compare like for like, at the same carat, colour, clarity and cut grade, and the gap will speak for itself.

Certification

This is where the three genuinely differ, and it is under discussed.

Both diamond types are graded to the same framework by the same laboratories: carat, colour on the D to Z scale, clarity, and a cut grade covering proportions, polish and symmetry. Lab grown reports come mostly from IGI, GIA and GCAL. Every lab grown diamond we set is IGI certified and laser inscribed on the girdle with its report number, which means the paper and the stone can be matched by anybody with a loupe, and the number can be checked on IGI's own website. What an IGI certificate tells you covers how to read one.

Moissanite certification works differently. Ours is GRC certified, which documents the stone and its specifications. It is real documentation and it is worth having, but it is not the same deep, universally standardised grading framework the diamond trade has built over decades, because moissanite is manufactured to a consistent standard rather than being sorted out of a random natural population. There is less variance to grade.

The practical upshot: with a diamond, the certificate is how you compare two stones and know you are not overpaying. With moissanite, the certificate confirms what you have, and the things to compare are the cut quality and the millimetre size.

Resale

None of the three holds its retail value, and anyone implying otherwise is selling.

Mined does least badly, and still badly. Lab grown prices have fallen substantially since 2020 as production scaled. Moissanite has never been sold on a value retention story, so nobody is disappointed.

The mechanism is the same for all three and it has nothing to do with the stone. A retail price includes the labour, the CAD and casting, the certification, the warranty, the premises, the marketing and ten per cent GST. A second hand buyer pays for the stone and the metal only, at the price they could replace them for. The rest does not come back, in any material. I have written this out properly in do lab grown diamonds hold their value, including what to do instead, which is to get the ring valued and specified on your contents insurance.

The narrow exception sits entirely on the mined side: fancy coloured stones, especially Argyle pinks since that mine closed in 2020, and signed period pieces. That is a collector market and it is not an engagement ring market.

Which should you buy

Keyed to situations rather than to what we stock.

You want diamond, and size and grade matter. Lab grown. Same material, same certificates, and the budget goes further in a way that changes what is actually achievable. This is most people.

Provenance genuinely matters to you. Mined, from someone who sells it. If you want a stone that formed underground over a billion years, you will not be talked out of it by a chemistry argument, and you should not be. Same answer if you are setting into an antique or period mounting, where a stone of the era is the point.

You want the largest, brightest stone for the smallest number. Moissanite. It is not a cheap diamond, it is a different stone with more fire, and if you like that look it is the best value on this page by a distance.

You work with your hands. Any of the three, but spend the saving on the setting. A bezel or a heavy claw setting, a shank at least around 1.8mm at the base, and platinum or 18ct rather than something thinner. The stone will outlive all of us. The setting is what fails.

You are buying to travel with it, or you lose things. Moissanite, or a lab grown stone at a size you can replace without pain. The replacement cost is the whole argument here.

You want an appreciating asset. None of these. Buy the ring you want and put the investment money somewhere designed to be an investment.

You are genuinely undecided between moissanite and lab grown. We sell both and we have no preference between them, which is the only reason to trust us on the question. Moissanite vs lab grown diamond sets the two side by side properly, including the optical differences in more detail than there is room for here.

The best way to settle it is to look at all three in person, because the fire difference in moissanite is the single thing that photographs badly and decides people instantly when they see it. We take appointments at the Southbank studio, and we run design consultations by video call for everyone else, with a free ring sizer sent before anything is cast. You can book an appointment either way.

FAQ

Is moissanite a fake diamond?

No. It is silicon carbide, a genuine mineral with its own properties, sold as itself. A fake diamond would be something sold as diamond that is not. Moissanite is 9.25 on the Mohs scale with more fire than diamond, and it is chosen by people who want that look, not by people trying to fool anyone.

Can you tell moissanite from diamond by looking?

At arm's length, usually not, especially under about 1ct. Under bright directional light and at larger sizes, the extra fire is visible if you know what to look for. A jeweller with a loupe identifies it in seconds by the doubled facet edges, because moissanite is doubly refractive and diamond is not.

Which lasts longest?

All three outlast you. Diamond is 10 on the Mohs scale and moissanite is 9.25, and both are far above anything they will meet in daily wear. The setting is what determines whether the ring lasts, not the stone.

Is lab grown diamond better than moissanite?

Neither is better. They are different materials for different priorities. Lab grown diamond is diamond, with the certificate and grading framework that comes with it. Moissanite is brighter, more fiery and much cheaper at size. We sell both and we do not have a preferred answer.

Do you sell mined diamonds?

No. We work in lab grown diamond and moissanite only. If a mined stone is what you want, you should buy it from a jeweller who deals in them, and you should ask them the resale question in this article and see what answer you get.