Mohs Hardness Scale Gemstones: Chart, Toughness and Care

On the Mohs hardness scale gemstones are ranked by one simple and very old idea: a harder mineral will scratch a softer one, and the softer one cannot scratch it back. That number, from 1 to 10, shapes a lot of everyday crystal life, from whether a stone can survive daily wear in a ring to how you should dust a raw specimen on your shelf.

This guide covers the ten reference minerals behind the scale, a chart of popular crystals and gems by number, why a hard stone can still chip, and practical care for each hardness band. Whether you collect smooth pocket stones or faceted jewelry, it is some of the most useful geology a crystal lover can learn.

What Is the Mohs Hardness Scale?

The Mohs scale of hardness of minerals was published in 1812 by the German mineralogist Friedrich Mohs, in a book meant to give naturalists a practical way to recognise minerals. The idea itself is much older. Around 300 BC Theophrastus wrote about comparing stones by what they could scratch, and Pliny the Elder came back to it in his natural history in the first century AD. What Mohs added was order. He picked ten familiar minerals, gave each one a number, and so made a ruler anyone could use.

Mohs hardness is a mineral’s resistance to being scratched. To place an unknown stone, you find the hardest reference mineral it can scratch and the softest one that can scratch it. If apatite (5) leaves a mark on your sample but fluorite (4) does not, the sample’s hardness is somewhere between 4 and 5. So when a guide tells you where on the Mohs hardness scale gemstones such as ruby or opal sit, it is reporting the result of this kind of side-by-side comparison.

For the scale, a “scratch” means a permanent groove you can see with the naked eye. A softer material can leave tiny, microscopic damage on a harder one, but that does not count when assigning a number. This detail matters later for storage.

Two things are worth knowing from the start. First, the scale is ordinal: it puts minerals in order but does not say how far apart they are. Second, it measures only one property, scratching. It tells you nothing about how a stone copes with a knock, heat or water, and those matter just as much for care.

The Ten Reference Minerals and Why the Gaps Are Uneven

Each step of the Mohs mineral hardness scale is anchored by a reference mineral, and most of them are common in ordinary rocks. Many are close relatives of stones you may already own.

The third column is the surprise. When the reference minerals are measured with a sclerometer, an instrument that gives an absolute value instead of a ranking, the steps turn out to be very uneven. Talc and gypsum are close neighbours. Corundum is roughly twice as hard as topaz, and diamond is nearly four times as hard as corundum. So the jump from 9 to 10 is huge, while the difference between a 7.5 and an 8 is small.

Keep that in mind whenever you compare where on the Mohs hardness scale gemstones fall. A sapphire at 9 and a diamond at 10 look like neighbours on paper, but for scratch resistance the diamond is in another league.

Half numbers, ranges and rocks

Most stones fall between two reference points. That is why you see values like 6.5, or ranges like 6 to 6.5. Natural material varies from piece to piece, and some minerals are listed with very wide spreads: kyanite, for example, is given anywhere from 4 to 7. One number is always a simplification.

Rocks add another complication. A mineral is a single natural solid, while a rock is a mixture of minerals, each with its own hardness. Lapis lazuli is a good example. It is a rock made mostly of blue lazurite, with brassy flecks of pyrite and white veins of calcite, which is why it is usually given a range of about 5 to 6 rather than one tidy figure. Granite is sometimes quoted at 6 to 7, but it is really a mosaic of quartz, feldspar and mica, and each of those has a different hardness.

Mohs Hardness Scale Gemstones Chart: Popular Stones by Number

The chart below groups well-loved gems and crystals from hardest to softest. The values are the figures commonly quoted in mineral references. Individual pieces can vary a little, and treated, dyed or composite stones may behave differently. A few everyday landmarks help with the numbers: window glass is about 5.5, ordinary steel about 4 to 4.5, copper about 2.5 to 3, and porcelain about 7.

Read down the list and a pattern appears: on the Mohs hardness scale gemstones that are valued for jewelry mostly sit between 6 and 10. The whole quartz family sits around 6.5 to 7, which helps explain why amethyst, agate and jasper have been carved, carried and worn for so long. The feldspar gems in our Moon & light collection sit just below quartz, at 6 to 6.5.

Further down the Mohs hardness scale gemstones give way to collector minerals. Many of these, such as vanadinite and wulfenite with their bright crystals, are prized for their colour and form, not for wearability. You will find many of them in our Earth treasures library.

Hardness vs Toughness: Why a Hard Stone Can Still Break

Hardness and toughness sound alike, but they describe different things. Hardness is resistance to scratching. Toughness is resistance to breaking, chipping or cracking when a stone is struck or dropped. A stone can be excellent at one and ordinary at the other.

Even at the top of the Mohs hardness scale gemstones are not indestructible. Diamond is the classic example. It tops the scale, yet a sharp blow in the wrong place can chip or split it, because high hardness can come with brittleness. Some softer materials, on the other hand, can absorb a knock without fracturing. That is why gemologists talk about overall durability, which combines three questions:

• Hardness: will everyday grit and contact scratch the polish?
• Toughness: will a knock chip or crack the stone?
• Stability: will heat, light, water or household chemicals change it?

Opal shows why the third question matters. It is hydrated silica, which means water is part of its make-up, and at 5.5 to 6.5 it is softer than quartz. If you love opal (the Australian Rainbow Tree opal is a spectacular example), treat it as a gem that rewards gentle handling, not one to toss in a bag with harder stones.

Wear can also come from below. Softer materials can leave microscopic damage on harder ones, so even a bag of quartz and agate pieces will slowly dull each other’s polish if they rattle around together for years.

Does hardness change a stone’s meaning?

In crystal traditions, where on the Mohs hardness scale gemstones sit does not decide their meaning. Meaning usually comes from colour, folklore and the ways people have used a stone over time. Still, many collectors find that hardness shapes how a stone fits into their practice.

Clear quartz, at 7, is often carried every day as a touchstone or kept on a desk during focused work. In crystal traditions it is believed to amplify intentions and to work well alongside other stones. Selenite, at 2, tends to stay put on a windowsill or altar, where many people use it as a calming visual anchor and associate it with clarity and gentle light. Some people like the symbolism in this: the enduring stone for steady daily intentions, and the delicate one as a quiet reminder to slow down and handle things with care.

Is a 7 Good? Using Hardness to Choose and Wear Stones

For everyday jewelry, 7 is a useful line: on the Mohs hardness scale gemstones at or above it cope with most casual contact. Quartz sits at 7, above window glass and ordinary steel, so brushing against keys, zips and door handles is less likely to leave a mark. That is why amethyst, citrine and other quartz gems make such dependable daily stones. Gems at 7.5 and above, including emerald, aquamarine, topaz, spinel, ruby and sapphire, have an extra margin.

Stones below 7 can still be worn. They just need a bit more thought. Moonstone, labradorite and opal make lovely pendants and earrings, which take far fewer knocks than rings and bracelets. Below about 5, most stones are best kept for display, meditation or occasional wear.

A worked example: choosing a stone for a daily ring

Here is how the Mohs hardness scale gemstones chart above plays out in a real choice. Imagine you want a ring to wear every day, and you are torn between amethyst, moonstone and turquoise.

• Amethyst (7): comfortable in almost any setting. It will take ordinary daily contact well, but it can still chip if you strike it hard against stone or metal.
• Moonstone (6 to 6.5): wearable, but softer than quartz. A bezel setting (a metal rim that wraps around the edge of the stone) protects it from side knocks, and taking the ring off for gardening, cleaning or the gym helps keep its glow.
• Turquoise (5 to 6): better as a pendant or earrings. On a hand it is likely to collect scratches and lose its polish within a few years of daily wear.

The same logic applies to bracelets. If you string quartz beads (7) next to fluorite beads (4), the quartz will slowly wear the fluorite as they rub together. Choose beads of similar hardness, or accept that the softer ones will age faster. If you are choosing a birth-month piece, our birthstone chart pairs well with this one.

A simple routine for any stone you plan to wear:

1. Look up its hardness and note whether it is a range.
2. Think about how it will be worn. Rings and bracelets take the most knocks, pendants and earrings fewer, display pieces almost none.
3. Check toughness and stability as well as the number.
4. For anything under 7 that you will wear often, choose a protective setting.
5. Plan where it will be stored and which stones it will touch.

How to Care for Gemstones by Hardness

Care follows naturally from where on the Mohs hardness scale gemstones sit. The basic rule is that a stone can be scratched by anything harder than itself, and that includes the other crystals in your collection.

Hard gems (8 to 10)

Diamond, ruby, sapphire, spinel and topaz shrug off most scratches, but they can scratch nearly everything else you own. Store them in separate pouches or a lined box with dividers. For cleaning, lukewarm water, a drop of mild soap and a soft brush work for most of them, followed by a rinse and a careful dry. Their main risk is impact, so take rings off before heavy work.

Quartz-band stones (6 to 7.5)

Amethyst, citrine, agate, jasper, tourmaline, garnet, moonstone and labradorite cope well with gentle care. Most can be wiped with a damp cloth and dried thoroughly. Tumbled stones (rough pieces rolled in a barrel with grit until they are smooth and rounded) are hardy, but they keep their shine longer in a cloth pouch than loose in a bowl with harder gems. Raw pieces, meaning stones left unpolished as they came from the ground, can have sharp edges and loose flakes, so handle them over a soft surface.

Soft stones (below 6)

At the soft end of the Mohs hardness scale gemstones and minerals need the most thought. Lapis lazuli, turquoise, fluorite, malachite, calcite, amber, pearl, vanadinite, wulfenite and selenite are best cleaned dry, with a soft brush or a lint-free cloth. Do not soak them. Selenite in particular should be kept away from water and damp rooms, and rough handling marks it easily.

Display pieces need their own care. A cluster is a group of crystals that grew together on a shared base, and a geode is a hollow rock whose inside is lined with crystals. Both are best dusted with a soft, dry brush or a gentle puff of air, and lifted by the base, never by the crystal points. If you keep clusters and geodes on open shelves, place them where they will not be knocked by doors or curtains. Polished spheres are safest on a stand or ring so they cannot roll.

Safety for people and pets

Avoid making crystal elixirs by soaking stones in water you plan to drink. Some minerals contain metals or other substances that do not belong in drinking water, and soft or porous stones can also be damaged by soaking. Keep small stones out of reach of children and pets, who might swallow them, and keep fragile raw specimens where a curious paw or hand cannot pull them down.

Can You Test a Stone’s Hardness at Home?

Field geologists still carry scratch kits to identify minerals roughly in the field. For polished gems and jewelry, though, the honest answer is not to test them. A scratch test damages the stone by design. Once a stone is identified, you can simply look up where on the Mohs hardness scale gemstones of that type sit. If you are unsure what a polished piece is, a gemologist can identify it without harming it.

For raw specimens where a tiny mark will not matter, a careful test can narrow things down:

1. Choose a hidden spot, such as the underside or back of the specimen.
2. Pick a reference with a known hardness: a glass plate (about 5.5), a steel nail (about 4 to 4.5), or a reference mineral.
3. Press firmly and draw one short line. Do not saw back and forth.
4. Wipe the spot with your finger. A softer material can leave a trail of its own powder that looks like a scratch but rubs away.
5. Check with a jeweler’s loupe (a small hand magnifier). A true scratch is a groove, not a smudge.
6. Test both ways: does the sample scratch the glass, and does the steel scratch the sample?
7. Write down a range. “Harder than steel, softer than glass” puts a stone at about 4.5 to 5.5.

Remember what the result can and cannot tell you. Scratching glass does not mean a stone is diamond or quartz, because everything above about 5.5 can do it, from feldspar to topaz. Hardness is one clue among several, alongside colour, lustre, crystal shape and weight.

If you would like to learn the scale without scratching anything, build a small reference tray. Some collectors start with a mixed set such as the crystal kits from Spirit Magicka, then label each piece they can identify with its hardness from the chart above. Over time, handling the stones side by side teaches you a lot about how soft and hard minerals look and feel.

Common Mistakes With Gem Hardness

• Treating hardness as toughness. A high number means scratch resistance, not chip-proof. Diamond can still break.
• Reading the scale as evenly spaced. The step from 9 to 10 is far bigger than the step from 1 to 2.
• Storing everything in one bag. Harder stones scratch softer ones, and even similar stones dull each other over time.
• Soaking soft or water-sensitive stones. Selenite, and other soft or porous stones, should be cleaned dry.
• Scratch-testing finished pieces. Look the stone up or ask a gemologist instead.
• Expecting a rock to have one hardness. Lapis lazuli and granite are mixtures, so their hardness varies across the surface.
• Trusting one figure for treated or composite material. Dyes, fillers and coatings can behave differently from the natural stone.

Once you know where on the Mohs hardness scale gemstones in your collection sit, wearing, storing and cleaning them becomes much simpler. Every stone in our crystal library pairs its traditional meanings with its mineral facts. If you are curious how gems and crystals differ, read what separates crystals from gemstones, and for the scarcer end of the mineral world, see our guide to rare gemstones and collector care. Our editorial approach explains how we write about crystal traditions alongside the geology. When you are ready to add a new piece to your shelf, Spirit Magicka is our own crystal shop.