Moissanite and diamond look similar face-up in most lighting conditions, which is exactly why the comparison has become central to conversations about engagement rings and fine jewellery. But the similarity ends at appearance. The two materials diverge across refractive index, hardness, dispersion, origin and price in ways that matter significantly depending on what the buyer is actually optimising for.
Optical properties: where moissanite actually exceeds diamond
Diamond has a refractive index of 2.417. Moissanite ranges from 2.65 to 2.69, giving it a higher brilliance potential in theory. Its fire, or dispersion, is also higher at 0.104 against diamond’s 0.044. In practice, this means moissanite in certain cuts and lighting conditions produces more coloured flashes than a diamond of equivalent size. For some buyers this reads as livelier; for others, especially those familiar with diamond, it reads as unnatural. A seasoned gemmologist will identify moissanite in seconds under a loupe because of its characteristic doubling of facet edges, caused by its double refractive nature. Diamond is singly refractive.
Hardness and durability over time
Diamond is the hardest natural material at 10 on the Mohs scale. Moissanite scores 9.25, harder than any coloured gemstone and harder than corundum. In practical daily wear, both will resist scratching from ordinary contact. The meaningful difference appears over decades: diamond maintains its polish indefinitely under normal conditions, while moissanite may develop minor surface abrasion in very long-term wear, though this is rarely significant in practice.
Origin, ethics and environmental framing
All gem-quality moissanite sold commercially is laboratory-grown. There is no meaningful natural supply. Natural moissanite was discovered in a meteorite crater and occurs in quantities too small for jewellery use. This makes moissanite’s environmental and ethical profile straightforward: no mining, no conflict chain, traceable production. Mined diamond carries a more complex supply chain, though certified conflict-free programmes such as the Kimberly Process have reduced the worst practices. Lab-grown diamond now sits alongside moissanite as a third option, with identical chemistry to mined diamond but laboratory origin.
Price and value retention
Moissanite costs roughly 10–15% of an equivalent mined diamond at retail. A one-carat laboratory-grown moissanite in an excellent cut typically sells for $300–600; a comparable mined diamond of equivalent grade sells for $4,000–8,000. Lab-grown diamond falls between the two, though its resale value has declined substantially as production scales. Mined diamond’s resale value remains more stable, particularly for larger, high-colour, high-clarity stones with origin certificates. Moissanite has essentially no resale market. It is valued for its utility at purchase, not as a financial asset.
The identification question
Standard diamond testers that measure thermal conductivity will misidentify moissanite as diamond. Moissanite’s thermal conductivity is close enough to trigger a positive reading. Moissanite-specific testers using electrical conductivity are required for reliable separation. A refractometer, doubling observation under 10x magnification, or spectroscopic analysis will distinguish the two definitively. Any gemmological laboratory will identify moissanite immediately. This matters for resale, insurance and any situation where the stone’s identity must be formally documented.
Which to choose
Choose moissanite if budget, environmental footprint and visual impact per dollar are the primary criteria, and the stone will not need to be appraised, resold or formally certified. Choose diamond, mined or laboratory, if the stone’s formal identity matters for insurance, legacy, certification or long-term value considerations. The comparison only becomes difficult when those priorities are mixed, which is exactly why it remains one of the most common conversations in contemporary fine jewellery.