Stones that resemble diamonds: moissanite and zircon

At a gem market in Jaipur, a vendor hands me a ring set with a sparkling colorless stone. "Diamond, madame. Special price for you." The brilliance is impressive, but the price, $240 for 2 carats, is enough to raise suspicion. Two minutes with a 10× loupe reveal the deception: a moissanite, a legal and beautiful stone in its own right, but sold for something it is not.

The market for Diamond alternatives is vast: moissanite, zircon, cubic zirconia, rock crystal, White Sapphire, colorless topaz. Some are rare natural gemstones, others sophisticated laboratory creations. All share one quality: their ability to mimic the brilliance of a Diamond, with varying degrees of resemblance. This guide details the physical, optical, and price differences to help you identify each stone and make an informed choice.

Moissanite is a silicon carbide (SiC) first discovered in 1893 by Henri Moissan inside a meteorite crater in Arizona. Natural moissanite is exceptionally rare; virtually all moissanite on the market today is synthetic, produced in laboratories since the 1990s. It is now the most visually convincing alternative to diamond available.

Moissanite has a refractive index of 2.65 to 2.69, higher than that of diamond (2.42). This elevated refraction produces an intense brilliance, sometimes described by gemologists as the "disco ball effect": the coloured fire (dispersion) is more pronounced than in a diamond. Its Mohs hardness of 9.25, just below diamond (10), makes it an exceptionally durable stone for everyday wear. Its density of 3.22 g/cm³ is slightly lower than that of diamond (3.52 g/cm³), meaning a moissanite weighs approximately 10% less than a diamond of the same size.

To the naked eye, a gem-quality moissanite can deceive the untrained observer. The distinguishing signs for an expert are: double refraction (moissanite is birefringent, unlike the singly refractive diamond; when viewing the back facets through the table with a 10× loupe, a slight doubling of the edges becomes visible), excessive dispersion (rainbow-coloured fire is more vivid under bright light), and a subtle tint (synthetic moissanites produced in the 1990s and 2000s often carried a yellow-green hue; more recent stones are nearly colourless, though under certain lighting conditions a faint nuance may still be perceptible).

In 2026, a one-carat moissanite is priced between £350 and £500, compared to £4,250 to £6,800 for a natural diamond of comparable quality (colour G-H, clarity VS2). The price ratio is approximately one to ten. Moissanite is openly marketed as an ethical and accessible alternative to diamond by brands such as Charles & Colvard, a pioneer in the field.

Zircon is a natural gemstone, a zirconium silicate (ZrSiO4), not to be confused with zirconium oxide, a synthetic stone discussed further below. Colourless zircon is rare and prized in gemology for its brilliance; it was in fact used as a Diamond simulant before the arrival of moissanite and zirconium oxide.

Zircon displays a refractive index of 1.81 to 2.02, depending on type: high, low, or intermediate zircon, and a dispersion of 0.039, slightly higher than that of a Diamond (0.044). This gives it a beautiful brilliance and pronounced colour dispersion. Its Mohs scale hardness is 6.5 to 7.5, which places it well below Diamond and moissanite; zircon can scratch over time and is not recommended for an everyday ring. Natural zircons sometimes display a very pronounced double refraction, visible to the naked eye on the back facets: a blurring or doubling effect that is never seen in a Diamond.

Natural colourless zircon is priced between £85 and £250 per carat, depending on origin and purity. Cambodian and Sri Lankan zircons are the most highly regarded. Today, it is primarily used in collector's jewellery or vintage pieces, less so in modern engagement rings, where its relative fragility can be a concern.

Cubic zirconia, commonly known as cubic zirconia or CZ, is a synthetic crystal of zirconium dioxide (ZrO₂) stabilised with yttrium. Developed in a laboratory in the USSR during the 1970s, it has become the world's most widely used diamond simulant, found in mass-market jewellery and fashion pieces.

Cubic zirconia has a refractive index of 2.15 to 2.18, lower than that of a diamond yet sufficient to produce a beautiful brilliance. Its Mohs hardness is 8 to 8.5, making it resistant, though not quite as durable as moissanite or diamond. Over time and with wear, a CZ may develop micro-scratches on its facets, gradually diminishing its brilliance. Its density of 5.6 to 6 g/cm³ is nearly twice that of a diamond, meaning a CZ of the same dimensions will weigh considerably more.

To the naked eye, a new CZ can shine with striking intensity. The tell-tale signs: excessive perfection (a CZ appears virtually flawless under a loupe, with no inclusions or imperfections; a natural diamond, even at a fine VS1-VS2 clarity, will always show inclusions visible under 10× magnification), less nuanced fire (the brilliance of a CZ is often described as "too white" or "too clean", lacking the depth and complexity of a diamond's fire), and thermal conductivity (by breathing a light mist onto the stone, a diamond will clear within 1 to 2 seconds; a CZ retains the condensation for 5 to 10 seconds. This test is not foolproof, as moissanite also passes it, but it does effectively rule out CZ).

A one-carat cubic zirconia costs less than £15. It is the most affordable simulant available, used extensively in costume jewellery and gold-plated pieces.

White Sapphire (colourless corundum, Al₂O₃) is a natural gemstone with a hardness of 9 on the Mohs scale, making it exceptionally durable. Its refractive index of 1.76 to 1.77 is notably lower than that of a diamond, producing a more understated brilliance. Dispersion is low (0.018), meaning little coloured fire. White Sapphire is a refined, restrained stone, sometimes chosen for minimalist engagement rings, yet it makes no attempt to imitate a diamond. It is a deliberate alternative, not a simulant. Price: £250 to £700 per carat depending on origin (Ceylon, Madagascar). Our collections favour coloured Sapphires (blue, pink, yellow), though White Sapphire remains an option for bespoke creations.

The colourless topaz (pure topaz, free of impurities) has a hardness of 8 on the Mohs scale and a refractive index of 1.61 to 1.63. Its lustre is vitreous, far less intense than that of a Diamond. Topaz is also vulnerable to impact and cleaves readily along certain crystalline planes. Price: £45 to £125 per carat.

Rock crystal is pure quartz (SiO₂), with a hardness of 7 on the Mohs scale. Its refractive index of 1.54 to 1.55 is very low, giving a dull lustre compared to a Diamond. It is an ornamental stone, never a credible simulant. Price: just a few pounds per carat.

The choice between a natural diamond and an alternative depends on your priorities: budget, ethics, durability, and symbolic meaning.

Diamond remains the preferred choice for pieces with strong symbolic significance (engagement rings, wedding rings) and for heirloom jewellery. Its exceptional durability (hardness 10 on the Mohs scale) ensures the stone will pass through generations without alteration. The brilliance of a fine-quality diamond, with its unique combination of brightness, controlled dispersion, and luminous depth, remains unmatched. Our collections favour certified natural diamonds for fine jewellery creations. Each diamond is selected by our gemologists according to the 4C criteria (carat, colour, clarity, cut) and accompanied by an authenticity certificate issued by an independent laboratory (GIA, HRD, IGI).

Moissanite is an excellent choice for those seeking diamond-like brilliance without the price, with a nearly indestructible stone (hardness 9.25 on the Mohs scale). It suits everyday rings, particularly for modern designs or travel pieces. Moissanite is also an ethical option: produced in a laboratory, it involves neither mining nor conflict zones. The White Sapphire is a understated alternative for minimalist designs, with durability close to that of a diamond. Natural colourless zircon appeals to collectors for its brilliance and rarity, yet its fragility makes it best suited to occasional wear. Cubic zirconia remains a costume jewellery choice, best avoided for pieces of value; its brilliance deteriorates over time and the stone lacks prestige.

No visual test alone can identify a stone with certainty. By combining several indicators, however, you can narrow down the possibilities.

The The fog test: breathe on the stone to coat it with condensation. A diamond disperses heat instantly, causing the fog to disappear within 1 to 2 seconds. A stone with low thermal conductivity (CZ, topaz, rock crystal) will retain the fog for 5 to 10 seconds. Note: moissanite also passes this test due to its high thermal conductivity, so it cannot be used to distinguish a diamond from a moissanite.

The 10x loupe test: examine the stone under a loupe. A natural diamond will always display internal inclusions (crystals, feathers, clouds), even in stones of fine clarity (VS1-VS2). A CZ is nearly flawless, with no visible imperfections. Moissanite will show doubling of the facet edges (double refraction) visible on the back facets.

The line test: place the stone table-side down on a sheet of white paper with a black line drawn on it. If you can clearly see the line through the stone, it is most likely not a diamond; the high refractive index of a diamond (2.42) bends light and renders the line invisible. Limitation: this test fails on poorly cut diamonds and is unreliable on stones that are already set.

The weight test: weigh the stone on a precision scale. Compare the measured weight to the expected weight of a diamond of the same dimensions (online calculators are available). A CZ weighs nearly twice as much as a diamond of the same size; moissanite weighs approximately 10% less. This test requires knowing the exact dimensions of the stone.

The only way to identify a stone with certainty is through a gemological certificate issued by an independent laboratory (GIA, HRD, IGI, SSEF). The certificate specifies the mineral species (diamond, moissanite, corundum, etc.), the origin (natural or synthetic), and any treatments applied. A certificate is most relevant for stones of a certain size, from 0.5 carat onwards for a diamond.

To learn more about reliable methods for identifying diamonds, consult our comprehensive guide.

The diamond simulant market raises a significant ethical concern: the deceptive sale of moissanites, CZ, or zircons as natural diamonds. This practice is illegal in France and across the European Union, yet it persists in travel markets, peer-to-peer resale platforms, and certain unscrupulous e-commerce sites.

Be wary of prices that seem too good to be true. A natural 1-carat diamond, G-H colour, VS2 clarity, excellent cut, is priced between £4,250 and £6,750 at a trusted jeweller. If someone offers you a "certified diamond" for £425, it is a scam. The certificate itself may be forged; always verify its authenticity online through the issuing laboratory's website (GIA, HRD, and IGI all maintain public verification databases).

With an established jewellery house, the risk is virtually non-existent. Reputable houses sell only identified, certified where appropriate, and fully traceable stones sourced directly from their suppliers. Our diamonds are individually inspected by our gemologists before setting. If you are purchasing outside a trusted channel, whether through a private sale, a gem market, or an unknown website, insist on a recent gemological certificate and verify it online before completing your purchase.

Transparency is a core principle at Mayuri: we always specify the stone's species (Diamond, Moissanite, Sapphire, and so on), its origin (natural or synthetic), and any treatments applied. An alternative stone sold as such is a perfectly legitimate choice. An alternative stone sold as a diamond is fraud.