Two of the most important durability properties for a gemstone are hardness and toughness — and they are not the same thing. A material can be extremely hard but brittle (diamond is an example). A material can be tough but soft. Moissanite scores exceptionally on both. This is the complete explanation.
Hardness vs. Toughness: The Distinction
Hardness is resistance to scratching — measured on the Mohs scale (1–10). A harder material scratches a softer one. Hardness determines whether a stone’s surface will dull or scratch from contact with other materials in daily wear.
Toughness is resistance to fracturing, chipping, and cracking under impact — measured in MPa·m¹⁄² (fracture toughness). A tougher material withstands impact without breaking. Toughness determines whether a stone survives being struck, dropped, or subjected to pressure.
These properties are independent: diamond is the hardest natural material (Mohs 10) but has relatively moderate toughness (2–4 MPa·m¹⁄²) and can chip or cleave along its crystal planes if struck at the right angle. Nephrite jade has Mohs hardness of only 6–6.5 but exceptional toughness (6–8 MPa·m¹⁄²) due to its interlocking fibrous crystal structure — it is very difficult to break even though it scratches easily. See our hardness guide.
Moissanite’s Hardness
Moissanite: Mohs 9.25 — the second hardest material used in jewelry after diamond. This means moissanite resists scratching from virtually every material it will contact in daily life: sand (quartz, Mohs 7), metal surfaces (typically Mohs 4–6), ceramic, glass, and other gemstones below 9.25. Only diamond (Mohs 10) and other moissanite stones can scratch moissanite. In practical terms, a moissanite stone worn daily for decades maintains its original surface polish without visible scratching. This is not true of softer alternatives such as cubic zirconia (Mohs 8.0–8.5) or even sapphire (Mohs 9.0). See our moissanite vs. CZ comparison.
Moissanite’s Toughness
Moissanite’s fracture toughness is approximately 7.6 MPa·m¹⁄² — significantly higher than diamond (2–4 MPa·m¹⁄²) and among the highest of any gemstone material. For comparison: sapphire ~2–3 MPa·m¹⁄²; ruby ~2–3 MPa·m¹⁄²; cubic zirconia ~2–3 MPa·m¹⁄².
This means moissanite is substantially more resistant to chipping and fracturing from impact than diamond, sapphire, or cubic zirconia. The strong covalent Si–C bonds in its crystal structure and the absence of cleavage planes (directions of atomic weakness along which a crystal preferentially breaks) make moissanite highly resistant to the kind of impact damage that can chip diamonds or fracture other gemstones.
Why Moissanite Doesn’t Have Cleavage Planes
Diamond has four directions of perfect cleavage — atomic planes along which the crystal splits cleanly under impact. This is why a struck diamond can cleave dramatically, and why diamond cutters use cleavage to split rough diamonds. Moissanite (SiC) does not have the same cleavage planes — it has no perfect cleavage. Instead, it fractures conchoidally (in a curved, shell-like pattern) when it fractures at all, requiring substantially more force than a cleaving diamond. In everyday jewelry-wearing conditions, this force is never encountered.
Practical Implications
A moissanite stone in a ring can be dropped on tile, struck against a hard surface, or catch on a door frame without chipping or fracturing — incidents that, in the same circumstances, could chip a diamond or fracture a sapphire. This makes moissanite particularly appropriate for daily-wear rings in active lifestyles, for buyers who work with their hands, or for anyone who wants a stone that is genuinely worry-free in normal life. See our lifetime durability guide and thermal properties guide.
Summary
Moissanite: Mohs 9.25 (scratch resistance) + fracture toughness 7.6 MPa·m¹⁄² (chip/fracture resistance) + no cleavage planes = the most comprehensively durable colorless gemstone available for daily-wear fine jewelry. It is harder than sapphire and significantly tougher than diamond.
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