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) discovered in 1893 by Henri Moissan inside a meteorite crater in Arizona. Natural moissanites are extremely rare; virtually all moissanites on the market are synthetic, produced in laboratories since the 1990s. Today, it is the most visually convincing alternative to Diamond.

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 colored flashes of light (dispersion) are more pronounced than in a Diamond. Its Mohs scale hardness is 9.25, just below Diamond (10), making 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 fool the uninitiated. 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 is visible), excessive dispersion (rainbow-colored flashes are more pronounced under bright light), and slight tint (synthetic moissanites from the 1990s and 2000s often displayed a yellow-green tint; more recent production is nearly colorless, though under certain lighting a subtle nuance may persist).

In 2026, a 1-carat moissanite costs between $480 and $720, compared to $6,000 to $9,600 for a comparable-quality natural 1-carat Diamond (color G-H, clarity VS2). The ratio is approximately 1 to 10. Moissanite is openly sold as an ethical and affordable 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 covered further on). Colorless zircon is rare and highly prized in gemology for its brilliance; it was widely used as a diamond simulant before the rise of moissanite and cubic zirconia.

Zircon displays a refractive index of 1.81 to 2.02 (depending on the type: high, low, or intermediate zircon) and a dispersion of 0.039, slightly lower than that of a diamond (0.044). This gives it a beautiful brilliance and vivid fire. Its Mohs hardness of 6.5 to 7.5 places it well below both diamond and moissanite; zircon can scratch over time and is not recommended for everyday wear rings. Natural zircons sometimes display a very pronounced double refraction, visible to the naked eye through the back facets as a blurring or doubling effect, something never found in a diamond.

Natural colorless zircon is priced between $120 and $350 per carat, depending on origin and clarity. Cambodian and Sri Lankan zircons are the most highly regarded. Today, zircon is primarily used in collector's jewellery and vintage pieces, less so in modern engagement rings, as its relative fragility presents a practical concern.

Zirconium oxide, commonly known as cubic zirconia or CZ, is a synthetic crystal of yttrium-stabilized zirconium dioxide (ZrO₂). Developed in a Soviet laboratory in the 1970s, it has since become the world's most widely used diamond simulant, found in mass-market jewellery and fashion pieces across the globe.

Cubic zirconia has a refractive index of 2.15 to 2.18, lower than that of a diamond, yet sufficient to produce a striking brilliance. Its Mohs hardness of 8 to 8.5 makes it durable, though not to the same degree as moissanite or diamond. Over time and with regular wear, a CZ may develop micro-scratches on its facets, gradually dulling its sparkle. 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 telltale signs of imitation: excessive perfection (a CZ is nearly flawless under a loupe, with no inclusions or imperfections; a natural diamond, even one of fine VS1-VS2 clarity, will always show inclusions under 10× magnification), less nuanced brilliance (the sparkle of a CZ is often described as "too white" or "too clean," lacking the depth and complexity of a diamond's fire), thermal conductivity (by breathing fog onto the stone, a diamond clears within 1 to 2 seconds; a CZ retains the fog for 5 to 10 seconds. This test is not foolproof, as moissanite also passes it, but it does rule out CZ).

A one-carat cubic zirconia costs under $25. It is the most affordable simulant, used extensively in costume jewellery and gold-plated pieces.

The White Sapphire (colourless corundum, Al₂O₃) is a natural gemstone with a hardness of 9 on the Mohs scale, making it highly durable. Its refractive index of 1.76 to 1.77 is noticeably lower than that of a diamond, resulting in a more understated brilliance. Dispersion is low (0.018), producing little coloured fire. White Sapphire is a refined, restrained stone, sometimes chosen for minimalist engagement rings. It does not seek to imitate the diamond; it is a confident alternative, not a simulant. Price: $350 to $950 per carat depending on origin (Ceylon, Madagascar). Our collections favour coloured Sapphires, blue, pink, and yellow, but 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. The brilliance is vitreous, far less intense than a diamond. Topaz is also vulnerable to impact, cleaving easily along certain crystalline planes. Price: $60 to $180 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 it a dull brilliance compared to a diamond. It is an ornamental stone, never a credible simulant. Price: a few dollars 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 market for diamond simulants raises a significant ethical concern: the deceptive sale of moissanite, CZ, or zircon as natural diamonds. This practice is illegal in France and across the European Union, yet it persists at travel markets, on peer-to-peer resale platforms, and through certain unscrupulous e-commerce websites.

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 $6,000 and $9,500 at a reputable jeweller. If someone is offering you a "certified diamond" for $600, it is a scam. The certificate itself may be forged; always verify the certificate's authenticity online through the laboratory's website (GIA, HRD, and IGI each maintain publicly accessible verification databases).

At an established jewellery house, the risk is virtually non-existent. Reputable houses sell only identified stones, certified where necessary, and fully traceable from the supplier. Our diamonds are individually inspected by our gemologists prior to setting. If you are purchasing outside of a trusted channel, whether through a private sale, a gem market, or an unknown website, always request a recent gemological certificate and verify it online before completing the purchase.

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