What the Mohs Scale Actually Measures

The Mohs hardness scale is one of those pieces of jewellery knowledge that repays a few minutes of your attention. Devised by the German mineralogist Friedrich Mohs in 1812, it ranks ten minerals from talc at 1 to diamond at 10, based on a simple principle: a harder material will scratch a softer one. Talc is so soft you can crumble it between your fingers; diamond will scratch practically anything.

The crucial thing to understand is that the scale is relative rather than linear. The gap in real hardness between 9 and 10 is far greater than the gap between 1 and 2, which is why diamond behaves so differently from corundum even though they sit only one step apart. What matters most for everyday wear, though, is a practical threshold: household dust commonly contains quartz at 7. Any gemstone softer than that will gradually collect micro-scratches from ordinary life — wiping, wearing, knocking against surfaces — and its surface will begin to look tired and cloudy rather than bright.

Why a Ring Demands More Than a Pendant

Not all jewellery faces the same risks. A pendant or a pair of drop earrings spends most of the day hanging quietly, protected by fabric and by the fact that your neck and ears rarely collide with brickwork. Rings are another matter entirely. Your hands are your tools: they grip door handles, lift shopping bags, tap keyboards, push trolleys, and reach into pockets where keys and coins are waiting.

Bracelets are similarly exposed, clattering against desks and each other throughout the day. So the same stone that thrives as a pendant might look scratched and dull within a year when set into a ring worn daily. Matching the stone to the setting is half the art of buying well.

A Practical Guide to Everyday Stones

Here is roughly how popular gemstones line up, and how much freedom each gives you:

• 9 to 10 — diamond, ruby, sapphire: the workhorses. Fine for rings worn every single day, including engagement and wedding bands.
• 8 to 8.5 — spinel, chrysoberyl, topaz: excellent durability. Topaz is hard but cleaves cleanly in one direction, so it dislikes sharp knocks.
• 7 to 7.5 — amethyst, citrine, smoky quartz, garnet, tourmaline, emerald: acceptable in rings with a little care. Emerald sits here on hardness but is notably brittle, so treat it gently.
• 6 to 6.5 — tanzanite, peridot, moonstone: better suited to earrings, pendants and occasional-wear rings than daily knocks.
• Below 6 — opal, turquoise, lapis lazuli, pearl, amber, coral: beautiful and delicate. Enjoy them in pieces that avoid the front line of daily wear.

As a rule of thumb, choose 8 or above for a ring you never intend to take off, 7 or above for a ring worn several times a week, and reserve the softer beauties for settings where they can shine without being tested.

Hardness Isn't the Whole Story

Hardness measures resistance to scratching, not resistance to breaking. Toughness — a stone's ability to withstand impact without chipping or cracking — is a separate quality, and some gems are surprisingly mismatched between the two. Jade, for instance, sits at only 6 to 7 on the scale yet is famously tough, which is why it has been carved into bangles for centuries. Emerald, at 7.5 to 8, is riddled with internal inclusions and can chip at the corners of a step cut if knocked against a table edge.

Cleavage matters too. Some minerals split neatly along internal planes, so a well-aimed blow can lift a corner clean off. Topaz and moonstone are the classic examples. Others, like opal, can craze — developing fine surface cracks — if exposed to sudden temperature changes or prolonged dryness. Knowing these quirks saves a great deal of heartache.

Caring for Gemstone Jewellery Day to Day

Good habits do more for longevity than any polish. Bearing in mind what we've covered, here is how to look after your pieces:

• Take rings off first before gardening, cleaning, DIY, gym sessions or swimming — chlorine and household bleach are unkind to many stones and to metal settings.
• Dress last, undress first: apply perfume, hairspray and moisturiser before putting jewellery on, and remove it before bed.
• Clean gently with warm water, a drop of mild washing-up liquid and a soft brush. Avoid ultrasonic cleaners and harsh dips for emerald, opal, pearl, tanzanite, turquoise and amber.
• Store pieces separately in soft pouches or compartmented boxes. A diamond rattling loose in a drawer will happily scratch everything around it.
• Check settings twice a year, particularly claws and the area around the girdle, and have loose stones tightened promptly.
• Wipe pearls and opals with a soft cloth after wearing, and have pearl strands restrung every few years if worn often.

Choosing With Confidence

Ask yourself two honest questions before you buy: how often will this be worn, and on which part of the body? A sapphire ring for a busy nurse and an opal pendant for weekend dinners are both perfectly sensible choices. Hardness is a guide, not a verdict — a softer stone worn thoughtfully can outlast a harder one that is neglected. Buy the piece you love, but let the Mohs scale help you decide where it belongs in your life.