When shopping for fine jewelry — especially pieces meant for everyday wear like engagement rings and wedding bands — durability is just as important as beauty. The Mohs hardness scale is the standard measure of a gemstone's ability to resist scratching, and understanding it is essential for making an informed purchase. Whether you're considering a diamond, moissanite, sapphire, or another gemstone, knowing where it falls on the Mohs scale will help you choose a stone that can withstand daily life.
What Is the Mohs Hardness Scale?
The Mohs hardness scale was created in 1812 by German geologist Friedrich Mohs. It ranks minerals on a scale from 1 to 10 based on their ability to scratch or be scratched by other materials. The scale is relative — meaning each mineral can scratch those below it and be scratched by those above it — but the intervals between numbers are not uniform.
How the Scale Works
The key principle is simple: a harder material will scratch a softer material, but not vice versa. For example, diamond (10) can scratch corundum (9), but corundum cannot scratch diamond. The scale uses ten reference minerals, each representing a specific hardness level.
Important Limitations
The Mohs scale has some important limitations to understand:
- It's relative, not linear: The difference between 9 and 10 is much larger than the difference between 1 and 2. Diamond is approximately four times harder than corundum (sapphire/ruby), even though they're only one point apart.
- It measures scratch resistance only: The scale doesn't account for a gemstone's resistance to breaking, chipping, or cracking (toughness).
- It doesn't measure durability comprehensively: A gemstone's overall durability depends on hardness, toughness, and stability.
The Complete Mohs Hardness Scale
| Mohs Rating | Mineral | Common Gemstone | Scratch Resistance |
|---|---|---|---|
| 1 | Talc | — | Very Poor |
| 2 | Gypsum | — | Poor |
| 3 | Calcite | — | Poor |
| 4 | Fluorite | — | Fair |
| 5 | Apatite | — | Fair |
| 6 | Orthoclase (Feldspar) | Moonstone, Labradorite | Good |
| 7 | Quartz | Amethyst, Citrine, Smoky Quartz | Good |
| 7.5 | — | Garnet, Tourmaline, Iolite, Zircon | Good |
| 8 | Topaz | Topaz (all colors) | Very Good |
| 8.5 | — | Spinel | Very Good |
| 9 | Corundum | Sapphire, Ruby | Excellent |
| 9.25 | — | Moissanite | Excellent |
| 9.5 | — | Boron Nitride (not a gemstone) | — |
| 10 | Diamond | Diamond (natural & lab) | Exceptional |
Gemstone Hardness Ranked: What You Need to Know
Mohs 10: Diamond
Diamond remains the undisputed king of hardness. It's approximately 58 times harder than corundum (9), making it virtually impossible to scratch under normal conditions. Only another diamond can scratch a diamond. This exceptional hardness is why diamonds are ideal for engagement rings and other jewelry subjected to daily wear.
Mohs 9.25: Moissanite
Moissanite ranks second among gemstones at 9.25 on the Mohs scale, making it one of the most durable diamond alternatives available. Its exceptional hardness means it's highly resistant to scratching and suitable for everyday wear in engagement rings. Moissanite's combination of hardness, brilliance (refractive index of 2.65–2.69), and affordability makes it a top choice for those seeking diamond alternatives. Learn more in our moissanite 4Cs grading guide.
Mohs 9: Corundum (Sapphire and Ruby)
Sapphire and ruby are both varieties of corundum, ranking at 9 on the Mohs scale. They're exceptionally durable and have been used in engagement rings and everyday jewelry for centuries. While they can be scratched by diamond or moissanite, this is unlikely to occur in normal wear. Blue sapphires are particularly popular as accent stones or center stones in engagement rings.
Mohs 8–8.5: Topaz and Spinel
Topaz (8) and spinel (8–8.5) offer good durability for most jewelry applications. They're suitable for occasional-wear rings, earrings, and pendants. For everyday rings, they may show some scratching over time but are generally durable enough with proper care.
Mohs 7–7.5: Quartz, Garnet, Tourmaline, and Zircon
Quartz varieties (amethyst, citrine, smoky quartz) rank at 7, while garnet, tourmaline, and zircon are slightly harder at 7–7.5. These gemstones are suitable for most jewelry but may accumulate scratches over years of daily wear in rings. They're better suited for earrings, pendants, and occasional-wear rings.
Mohs 6–6.5: Feldspar (Moonstone, Labradorite)
Feldspar minerals like moonstone and labradorite rank at 6–6.5 on the Mohs scale. While beautiful, they're relatively soft and prone to scratching. They're best suited for earrings and pendants rather than rings. If used in rings, protective settings like bezels are recommended.
Below Mohs 6: Not Recommended for Rings
Gemstones below 6 on the Mohs scale — including fluorite (4), calcite (3), and opal (5.5–6.5) — are generally not recommended for rings, especially engagement rings. They scratch easily and require significant care to maintain their appearance.
Hardness vs. Toughness vs. Stability
The Mohs hardness scale measures only one aspect of a gemstone's durability. To fully understand durability, you need to consider three factors:
Hardness
Hardness is resistance to scratching, measured by the Mohs scale. This is the most commonly cited durability metric.
Toughness
Toughness is resistance to breaking, chipping, and cracking. This depends on the gemstone's crystal structure and cleavage properties:
| Gemstone | Hardness | Toughness | Notes |
|---|---|---|---|
| Diamond | 10 | Good | Has perfect cleavage in 4 directions; can chip if struck |
| Moissanite | 9.25 | Excellent | No cleavage; highly resistant to breaking |
| Sapphire | 9 | Excellent | No cleavage; very tough |
| Topaz | 8 | Poor | Perfect basal cleavage; chips easily |
| Zircon | 7.5 | Fair to Poor | Brittle; prone to chipping |
| Opal | 5.5–6.5 | Very Poor | Prone to cracking and crazing |
Notably, while diamond is the hardest gemstone, it's not the toughest. Diamond has perfect cleavage in four directions, meaning a sharp blow in the right direction can split it. Moissanite, with no cleavage planes, is actually more resistant to breaking.
Stability
Stability refers to a gemstone's resistance to chemical changes, heat, and light:
- Diamond: Excellent stability; resistant to most chemicals and heat
- Moissanite: Excellent stability; highly resistant to heat and chemicals
- Sapphire: Excellent stability
- Emerald: Moderate stability; sensitive to heat and chemicals
- Opal: Poor stability; sensitive to heat (can crack) and dehydration (can craze)
- Pearl: Poor stability; sensitive to acids, perfumes, and cosmetics
Which Gemstones Are Suitable for Engagement Rings?
For engagement rings and other everyday-wear jewelry, we recommend gemstones with a Mohs hardness of 8 or higher. Here's our ranking:
Tier 1: Excellent for Daily Wear (9+)
| Gemstone | Mohs Hardness | Recommendation |
|---|---|---|
| Diamond | 10 | Ideal for all jewelry types |
| Moissanite | 9.25 | Ideal; excellent diamond alternative |
| Sapphire | 9 | Ideal for all jewelry types |
| Ruby | 9 | Ideal for all jewelry types |
Tier 2: Good for Daily Wear (8–8.9)
| Gemstone | Mohs Hardness | Recommendation |
|---|---|---|
| Spinel | 8 | Suitable with care |
| Topaz | 8 | Suitable but has cleavage concerns |
Tier 3: Moderate Wear Only (7–7.9)
| Gemstone | Mohs Hardness | Recommendation |
|---|---|---|
| Garnet | 7–7.5 | Occasional wear in rings |
| Tourmaline | 7–7.5 | Occasional wear in rings |
| Quartz | 7 | Not ideal for engagement rings |
Below 7: Not Recommended for Rings
Gemstones below 7 on the Mohs scale should be reserved for earrings, pendants, and other jewelry that doesn't receive daily wear.
How to Protect Your Gemstone Jewelry
Even the hardest gemstones can be damaged. Here's how to protect your jewelry:
- Remove before physical activity: Take off rings before exercising, gardening, or doing manual labor
- Store separately: Keep gemstones from scratching each other by storing in separate compartments or pouches
- Avoid extreme temperatures: Rapid temperature changes can cause thermal shock, even in hard stones
- Clean gently: Use warm water, mild soap, and a soft brush
- Get regular check-ups: Have a jeweler inspect prongs and settings annually
Frequently Asked Questions
Is moissanite hard enough for an engagement ring?
Absolutely. At 9.25 on the Mohs scale, moissanite is one of the hardest gemstones available and is perfectly suited for everyday wear in engagement rings. It's significantly harder than sapphire (9) and approaches diamond's hardness (10). For more information, see our diamond alternatives comparison.
Can a diamond be scratched?
Only another diamond can scratch a diamond. However, diamond can still be chipped or cracked if struck hard enough in the right direction due to its cleavage planes. Always protect diamond jewelry from hard impacts.
What's the difference between hardness and toughness?
Hardness measures resistance to scratching (Mohs scale), while toughness measures resistance to breaking and chipping. A gemstone can be very hard but not very tough (like diamond, which has perfect cleavage) or vice versa. Moissanite is notable for being both hard (9.25) and tough (no cleavage).
Does the Mohs scale measure linearly?
No. The Mohs scale is relative, not linear. The difference between 9 and 10 (corundum to diamond) is much larger than the difference between 1 and 2 (talc to gypsum). Diamond is approximately four times harder than corundum, even though they're only one point apart.
Conclusion
The Mohs hardness scale is an essential tool for understanding gemstone durability and making informed jewelry purchases. For engagement rings and everyday-wear pieces, choosing a gemstone with a Mohs rating of 8 or higher — ideally 9 or above — ensures your jewelry will maintain its beauty for years to come.
Diamond (10), moissanite (9.25), and sapphire (9) stand out as the best choices for durability, offering the scratch resistance needed for daily wear. By understanding hardness, toughness, and stability, you can select a gemstone that not only looks beautiful today but will continue to sparkle for generations.
Ready to find a durable, beautiful gemstone? Explore our collection of moissanite engagement rings and discover stones built to last a lifetime.