Moissanite vs. Natural Diamond: The Complete Scientific Comparison 2026

September 4, 2026

The comparison between moissanite and natural diamond is most often framed in terms of price and appearance. But the most important differences — and the most important similarities — between these two materials are physical and optical, rooted in the fundamental differences in their crystal structures and chemical compositions. This guide presents the complete scientific comparison, so you can make an informed decision based on what these materials actually are rather than marketing claims from either direction.

Crystal Structure and Chemical Composition

Diamond: Diamond is pure carbon (chemical formula C) arranged in a face-centered cubic crystal lattice — a tetrahedral arrangement in which each carbon atom is bonded to four neighboring carbon atoms in a rigid, three-dimensional network. This arrangement is the strongest possible atomic bonding configuration for carbon, which is why diamond is the hardest naturally occurring material on Earth.

Moissanite: Moissanite is silicon carbide (chemical formula SiC) — a compound of silicon and carbon arranged in a hexagonal (6H polytype) or cubic (3C polytype) crystal lattice. The most common polytype used in jewelry-grade moissanite is 6H-SiC, which has a hexagonal crystal structure. The silicon-carbon bonds in moissanite are extremely strong — not as strong as diamond's carbon-carbon bonds, but stronger than the bonds in nearly every other gemstone material.

The difference in crystal structure has several practical consequences that flow through every other physical property comparison below.

Hardness (Mohs Scale)

Diamond: 10 (the maximum)
Moissanite: 9.25

Diamond is the hardest material on the Mohs scale — nothing in nature scratches diamond except another diamond. Moissanite at 9.25 is the second hardest gemstone material used in jewelry, harder than sapphire (9.0), ruby (9.0), and every other colored gemstone. In practical daily wear terms, both diamond and moissanite are scratch-resistant to all common environmental materials (metal, glass, ceramic, dust particles). The 0.75-point Mohs difference between moissanite and diamond has no meaningful practical consequence for daily wear durability. Read more: Can Moissanite Get Scratched?

Refractive Index

Diamond: 2.417–2.419
Moissanite: 2.650–2.690

The refractive index (RI) measures how much a material bends light as it passes through the stone. A higher RI means light is bent more sharply, which translates to more intense white light return (brilliance) when the stone is cut to correct proportions. Moissanite's RI of 2.65–2.69 is higher than diamond's 2.42 and higher than any other gemstone used in fine jewelry. This means a well-cut moissanite produces more intense brilliance — more white light reflected back to the viewer's eye — than an equivalent diamond. Read more: Moissanite vs. Diamond Brilliance Visual Guide.

Dispersion (Fire)

Diamond: 0.044
Moissanite: 0.104

Dispersion measures a material's ability to split white light into its spectral components — the rainbow flashes of color visible in a stone, known as fire. Moissanite's dispersion of 0.104 is 2.4 times higher than diamond's 0.044 — the highest dispersion of any gemstone used in fine jewelry. This is why moissanite produces significantly more colored fire than diamond. Some buyers find this additional fire desirable; others prefer the more subdued fire of diamond. Both are legitimate aesthetic preferences. The fire difference is most visible in direct sunlight and becomes less pronounced in diffuse indoor lighting. Read more: Why Moissanite Has More Fire Than Diamond.

Thermal Conductivity

Diamond: 900–2,320 W/m·K (the highest of any material)
Moissanite: 490–500 W/m·K

Thermal conductivity is the most important physical difference between moissanite and diamond from a testing perspective. Diamond conducts heat at extraordinary rates — higher than any other material — which is the basis of the diamond tester: a device that measures thermal conductivity to identify diamond. Moissanite's thermal conductivity (490–500 W/m·K) is high enough that older single-probe thermal diamond testers register moissanite as diamond. Modern dual-probe testers (electrical conductivity + thermal conductivity) correctly distinguish moissanite from diamond. Read more: Does Moissanite Pass a Diamond Tester?

Birefringence

Diamond: None (isotropic — single refraction)
Moissanite: Present (anisotropic — double refraction)

Diamond's cubic crystal structure is optically isotropic — light passes through it at the same speed in all directions. Moissanite's hexagonal crystal structure is optically anisotropic — it produces two slightly different refractive indices depending on the direction of light travel (ordinary ray RI: 2.65; extraordinary ray RI: 2.69). Under 10x magnification with a loupe, this birefringence is visible as a subtle doubling of the back facets' edges when viewed through the table — the primary optical method for distinguishing moissanite from diamond under magnification. This effect is not visible to the naked eye in normal wear conditions.

Summary: What Each Difference Means for Your Decision

Hardness: Both are excellent for daily wear. No practical difference.
Brilliance: Moissanite produces more intense white light return. Advantage: moissanite.
Fire: Moissanite produces significantly more colored fire. Advantage depends on personal preference.
Thermal conductivity: Diamond's is higher — relevant only for tester identification, not for wear.
Birefringence: Visible under magnification; not visible to the naked eye in wear.
Price: Moissanite is 85–95% less expensive than an equivalent-sized natural diamond. Read more: The Economics of Smart Luxury.