Gemstone Education

The Mohs hardness scale: a complete guide to gemstone durability

The Colored Stone Co. · May 2026 · 10 min read

If you're choosing a gemstone for an engagement ring or any piece of jewellery you'll wear every day, hardness matters more than most people realise. A stunning stone that scratches easily won't look stunning for long. The Mohs hardness scale is the standard tool gemologists use to measure how resistant a mineral is to scratching — and understanding it takes about five minutes.

This guide covers what the Mohs scale is, where every major gemstone sits on it, and — most importantly — what those numbers actually mean when you're choosing a stone for a ring, pendant, or pair of earrings.

What is the Mohs hardness scale?

The Mohs scale was created in 1812 by German mineralogist Friedrich Mohs. It ranks ten common minerals from 1 (softest) to 10 (hardest), based on which mineral can scratch which. A mineral higher on the scale will scratch anything below it, but nothing above it.

The scale is ordinal, not linear. That's the most important thing to understand. The gap between 9 and 10 is vastly larger than the gap between 1 and 2. Diamond (10) is roughly four times harder than sapphire (9) in absolute terms — even though they sit just one number apart. Each step up represents a significant jump in scratch resistance.

What the Mohs scale means for your jewellery

Hardness isn't just a laboratory number — it directly affects how well your jewellery holds up over years of wear. Different pieces take different levels of daily punishment, and the right gemstone depends on where you'll wear it.

RINGS (HIGH WEAR)

Your hands touch everything — door handles, keyboards, gym equipment, kitchen surfaces. Rings take the most contact of any jewellery type. For engagement rings and wedding bands worn every day, Mohs 9 or 10 is ideal. That means sapphires (9) and diamonds (10) — both are practically scratch-proof in daily life.

EARRINGS AND PENDANTS (LOW WEAR)

Earrings and pendants rarely touch hard surfaces, so softer stones work well. Tanzanite (6.5), moonstone (6), and opal (5.5–6.5) are all beautiful choices for pieces that hang freely rather than take daily contact.

BRACELETS (MODERATE WEAR)

Bracelets sit on your wrist and occasionally bump against desks and surfaces. Mohs 7 and above is a safe choice. Spinel (8), topaz (8), and garnet (7–7.5) all handle bracelet wear without issue.

Gemstones we work with and their Mohs hardness

At The Colored Stone Co., we primarily work with gemstones rated Mohs 8 and above — stones that are built to last in rings worn every day. Here's how the gemstones in our range perform on the hardness scale.

DIAMOND — MOHS 10

The hardest natural substance on earth. Nothing can scratch a diamond except another diamond. This makes it the most durable gemstone for any type of jewellery, from diamond engagement rings to everyday pieces. Both natural and lab-grown diamonds share the same Mohs 10 rating — they're chemically and physically identical.

SAPPHIRE AND RUBY — MOHS 9

Sapphires and rubies are both varieties of the mineral corundum, and both rate Mohs 9. That makes them the second-hardest gemstones used in jewellery — harder than virtually everything you'll encounter in daily life. Ceylon sapphires come in Blue, Pink, Violet, Yellow, and White, and every colour shares the same exceptional hardness. This is one of the reasons sapphires are considered the ideal alternative to diamonds for engagement rings.

CHRYSOBERYL AND ALEXANDRITE — MOHS 8.5

Chrysoberyl — including the rare colour-changing alexandrite — sits at Mohs 8.5. This places it between sapphire and spinel in hardness, making it excellent for rings and everyday wear. Sri Lanka is one of the world's most important sources of chrysoberyl, and these stones offer something most gemstones cannot: a visible colour shift between daylight and artificial light.

SPINEL — MOHS 8

Spinel has been quietly prized by gemologists for centuries — historically confused with rubies and sapphires because it appears in similar colours and is nearly as hard. At Mohs 8, spinel is durable enough for daily-wear rings and requires no special care. It's particularly sought after in cobalt blue, a vivid hue that rivals the finest sapphires.

Hardness vs toughness: they're not the same thing

This is where many people get confused. Hardness measures scratch resistance. Toughness measures resistance to chipping, cracking, or breaking on impact. A gemstone can be very hard but not particularly tough.

Diamond is the hardest substance known (Mohs 10), but it has perfect cleavage planes — meaning a sharp blow at the right angle can split it. A sapphire (Mohs 9) has no cleavage and is considered excellent in toughness, making it arguably the most durable all-round gemstone for jewellery. Jade, at only Mohs 6–7, is one of the toughest gemstones in existence due to its interlocking crystal structure.

For everyday jewellery, you want both high hardness and good toughness. Sapphires and rubies (Mohs 9, excellent toughness) deliver both. Diamonds (Mohs 10, good toughness) are close behind. Spinel (Mohs 8, good toughness) rounds out the top tier.

Why sapphires are the jeweller's favourite for engagement rings

There's a reason sapphires have been the gemstone of choice for royalty and engagement rings for centuries, and it's not just their colour. At Mohs 9 with excellent toughness and no cleavage, sapphires are the most durable coloured gemstone you can put in a ring. They resist scratches from virtually everything in daily life, they don't chip easily, and they maintain their polish for decades.

Ceylon sapphires — mined in Sri Lanka — are considered among the finest in the world. They're available in Blue, Pink, Violet, Yellow, and White, giving you the colour range of many different gemstones with the durability of just one. Every colour of sapphire rates the same Mohs 9.

For buyers comparing a diamond vs sapphire engagement ring, the hardness difference (10 vs 9) is negligible in practical terms. Both are scratch-proof against anything you'll encounter in daily life. The real difference comes down to colour preference and budget.

How to care for gemstones based on their hardness

Understanding where your stone sits on the Mohs scale tells you exactly how to care for your jewellery. The golden rule: harder stones can scratch softer ones, so store each piece separately.

MOHS 9–10 (DIAMOND, SAPPHIRE, RUBY)

The most low-maintenance stones. Clean with warm soapy water and a soft brush. Ultrasonic cleaners are generally safe (unless the stone has significant inclusions or fracture filling). Store separately — a diamond can scratch a sapphire, and both will scratch everything else in your jewellery box.

MOHS 7–8.5 (SPINEL, CHRYSOBERYL, TOPAZ, GARNET)

Still durable, but avoid abrasive cleaners. Warm soapy water is ideal. Remove rings in this range before heavy manual work. Store away from harder stones.

MOHS 5–7 (OPAL, TANZANITE, MOONSTONE, PERIDOT)

Handle with care. These stones scratch relatively easily and should be reserved for earrings, pendants, or occasional-wear rings. Clean gently with a damp cloth — no ultrasonic cleaners, no harsh chemicals. Store individually in soft pouches.

Frequently asked questions about the Mohs hardness scale