Moissanite and cubic zirconia are both frequently described as “diamond alternatives,” and the comparison ends there. In nearly every measurable physical property, they are dramatically different materials with dramatically different performance in jewelry. This is the complete scientific comparison.
Hardness: Mohs Scale
Moissanite: 9.25 Mohs. Cubic zirconia: 8.0–8.5 Mohs. Diamond: 10 Mohs.
The Mohs scale is logarithmic, not linear — the difference between 8.5 and 9.25 is substantially larger than the numbers suggest. In practical terms: cubic zirconia scratches from airborne dust particles (which contain quartz at Mohs 7), from contact with other jewelry, and from daily abrasion over months of wear. A cubic zirconia stone worn daily will show visible surface scratching within 1–2 years, progressively dulling its brilliance. Moissanite at 9.25 resists scratching from virtually every material it will encounter in daily life except diamond. A moissanite stone worn daily for decades retains its original surface finish. See our complete hardness guide.
Refractive Index & Brilliance
Moissanite: RI 2.65–2.69. Cubic zirconia: RI 2.15–2.18. Diamond: RI 2.42.
Refractive index determines how strongly a material bends light — higher RI means more light returned to the eye as brilliance. Moissanite’s RI of 2.65–2.69 exceeds even diamond’s 2.42, giving it exceptional brilliance. CZ’s lower RI of 2.15–2.18 produces noticeably less brilliance — particularly visible in side-by-side comparison and under mixed lighting conditions.
Dispersion & Fire
Moissanite: dispersion 0.104. Cubic zirconia: dispersion 0.060. Diamond: dispersion 0.044.
Dispersion creates the rainbow fire flashes visible in a cut stone. Moissanite’s dispersion of 0.104 is 2.4x diamond’s and 1.7x cubic zirconia’s — producing the most fire of any colorless gemstone in regular jewelry use. CZ produces more fire than diamond but significantly less than moissanite. See our complete dispersion guide.
Thermal Conductivity
Moissanite: ~490 W/m·K. Cubic zirconia: ~2 W/m·K. Diamond: ~900–2,320 W/m·K.
This is the property that causes thermal diamond testers to read moissanite as diamond and CZ as “not diamond.” CZ’s extremely low thermal conductivity — 245x lower than moissanite — means it retains heat rather than dissipating it. In practical terms, this also means CZ is more vulnerable to thermal shock from rapid temperature changes. See our thermal conductivity and testing guide and our thermal expansion guide.
Density & Weight
Moissanite: density 3.21 g/cm³. Cubic zirconia: density 5.6–6.0 g/cm³. Diamond: 3.52 g/cm³.
CZ is nearly twice as dense as moissanite. A CZ stone of the same carat weight as a moissanite stone is physically smaller — carat is a unit of weight, not size. A 1-carat CZ is visually smaller than a 1-carat moissanite. Alternatively, a CZ stone of the same physical dimensions as a 1-carat moissanite will weigh approximately 1.75 carats — significantly heavier in a ring setting. See our specific gravity and weight guide.
Long-Term Wearability
This is where the comparison is most decisive. Moissanite worn daily for 10, 20, or 30 years retains its original brilliance, fire, and surface finish — it carries a lifetime gemstone warranty for exactly this reason. Cubic zirconia worn daily begins showing visible surface scratching within months, progressively clouding and dulling over 1–2 years until it requires replacement. CZ is not a long-term fine jewelry stone — it is a fashion stone with a finite useful life in daily-wear settings. See our lifetime durability guide and our does moissanite get cloudy guide.
Price Comparison
CZ is substantially cheaper than moissanite at point of purchase. However, CZ in daily-wear fine jewelry settings requires periodic stone replacement as it scratches and dulls — adding replacement cost over time. Moissanite’s higher upfront cost is offset by its permanent durability: one purchase, one stone, no replacement. For buyers choosing between the two for a piece intended for regular wear, moissanite’s lifetime cost is lower. See our budget guide.
The Summary Table
Hardness: Moissanite 9.25 vs CZ 8.0–8.5
Refractive Index: Moissanite 2.65–2.69 vs CZ 2.15–2.18
Dispersion: Moissanite 0.104 vs CZ 0.060
Thermal Conductivity: Moissanite ~490 W/m·K vs CZ ~2 W/m·K
Density: Moissanite 3.21 g/cm³ vs CZ 5.6–6.0 g/cm³
Daily Wear Lifespan: Moissanite lifetime vs CZ 1–2 years before visible dulling
For a comparison with diamond specifically, see our moissanite vs. diamond guide.
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