Minerals on Mohs Hardness Scale: The 10 Reference Stones

The minerals on Mohs hardness scale charts are ten fairly ordinary stones, running from soft, soapy talc to diamond, and together they answer one surprisingly useful question for anyone who loves crystals: what will scratch what? Knowing the order helps you identify an unknown stone, choose jewelry that will survive daily wear, and store a collection so the hard pieces do not quietly scuff the soft ones. This guide walks through each reference mineral, explains why the numbers are less tidy than they look, and shows you how to run a careful scratch test at home.

What is the Mohs hardness scale?

The Mohs scale ranks minerals by scratch resistance: a harder material can scratch a softer one, but not the other way round. It was introduced in 1812 by the German geologist and mineralogist Friedrich Mohs, in a book whose title translates roughly as Attempt at an Elementary Method for the Natural-Historical Determination and Recognition of Fossils. Mohs chose ten minerals, numbered them 1 to 10, and invited anyone to compare an unknown sample against them.

The idea itself is far older than Mohs. The Greek writer Theophrastus described comparing stones by which could scratch which in his treatise On Stones, around 300 BC, and Pliny the Elder returned to it in his Natural History around AD 77. What Mohs added was a fixed set of reference points, most of them minerals that are common in ordinary rocks and easy to obtain. Only diamond, at the top, was ever hard to come by.

Two words help when reading any chart:

• Mohs hardness is the number a mineral receives on this scale. It measures resistance to scratching, not to breaking or chipping.
• Ordinal means the scale ranks minerals in order without saying how far apart they are. Quartz (7) is harder than feldspar (6), but the scale alone does not tell you by how much.

Minerals versus rocks

You will often see the phrase “Mohs rock hardness scale”, but the scale is really built for minerals. A mineral is a naturally occurring, chemically defined solid; a rock is a mixture of one or more minerals. Granite is sometimes given a hardness between 6 and 7, yet a single piece can contain quartz (7), orthoclase feldspar (6), plagioclase (6 to 6.5) and mica (2 to 4), so different spots on the same stone scratch differently. When a rock receives one number, treat it as a rough average rather than a precise reading.

The 10 minerals on Mohs hardness scale charts

Here are the ten reference minerals on Mohs hardness scale charts, with their chemical formulas and an “absolute hardness” figure measured with an instrument called a sclerometer. That last column shows how hard each mineral really is relative to the others, with quartz set at 100.

A popular memory aid strings the names together in order: Talc, Gypsum, Calcite, Fluorite, Apatite, Feldspar, Quartz, Topaz, Corundum, Diamond. Many collectors invent their own sentence from the first letters; the sillier it is, the better it sticks.

1. Talc

Talc is pale, often white, grey or soft green, and feels greasy or soapy to the touch. It is a magnesium silicate, and it is so soft that a fingernail leaves a mark. Soapstone, a rock rich in talc, has been carved for centuries for exactly this reason. In crystal traditions talc turns up rarely, but where it does it is associated with gentleness and ease. Store it alone, out of pockets and away from other stones.

2. Gypsum

Gypsum is a hydrated calcium sulfate, meaning water is built into its crystal structure. It forms clear blades, satiny fibrous bundles and rosette shapes, and many crystal lovers know it in its clear, glassy variety, selenite. A fingernail can usually scratch it. In crystal traditions the clear forms are linked with light, clarity and calm, and people often place them on a shelf or windowsill rather than carrying them. Keep gypsum dry and handle it as little as possible, since it marks very easily.

3. Calcite

Calcite is calcium carbonate, the same compound that builds limestone and marble. It comes in a wide range of colours and often breaks into neat rhombic shapes. A copper coin sits close to calcite in hardness, so it is a classic test of whether a stone is above or below 3. Many people use calcite in meditation as a stone of gentle encouragement. Avoid acidic cleaners and rough handling, and keep it away from harder neighbours.

4. Fluorite

Fluorite, calcium fluoride, often grows as cubes and is loved for its purple, green and banded colouring. It also splits cleanly along flat planes, so it can chip even though it is not the softest stone here. Crystal traditions associate fluorite with focus and mental order, and many people keep a piece on a desk. Its hardness of 4 means steel can scratch it, so do not tumble it with quartz or keep it loose in a bag of mixed stones.

5. Apatite

Apatite is a calcium phosphate found in blue, green, yellow and other shades. It sits just below glass in hardness, which makes it the turning point in many home tests. In crystal traditions apatite is linked with motivation and communication. As a jewelry stone it is best in pendants or earrings rather than rings, where daily knocks and abrasion would dull it.

6. Orthoclase feldspar

Orthoclase is a potassium aluminium silicate and one of the feldspars, the most widespread mineral family in the Earth’s crust. Specimens are often creamy, pink or salmon coloured with a slightly pearly lustre. At 6 it can scratch ordinary glass. Feldspars appear throughout crystal traditions, often linked with self-awareness and new beginnings. You can find feldspar relatives and many other non-quartz stones on our Earth treasures shelf.

7. Quartz

Quartz is silicon dioxide and the benchmark of the whole scale: it is common, hard and found in almost every environment. Amethyst, citrine, agate, carnelian and onyx are all forms of quartz, which is why our Quartz & family section is so large, and why the many types of quartz deserve their own guide. Crystal traditions treat clear quartz as an all-purpose stone said to amplify intention. Its hardness makes it a good choice for everyday jewelry. If you would like a reference piece of your own, Spirit Magicka is the journal’s own crystal shop.

8. Topaz

Topaz is an aluminium silicate containing fluorine and hydroxide, prized as a gemstone in many colours. It is hard enough to scratch quartz, but it has a direction of easy splitting, so a sharp knock can cleave it. In crystal traditions topaz is linked with warmth, generosity and clear communication. Set in jewelry, it deserves a protective setting and a separate pouch.

9. Corundum

Corundum is aluminium oxide, and its gem forms are ruby and sapphire. Sapphire sits at 9, which is why it survives decades of wear in rings. Traditions link sapphire with wisdom and loyalty and ruby with passion and vitality. Corundum is hard enough to scratch nearly every other stone in your collection, so store it apart from softer pieces.

10. Diamond

Diamond is pure carbon arranged in an extremely tight crystal structure. It was the hardest naturally occurring mineral known when Mohs built his scale, so it sets the top at 10. The very word “adamant”, meaning unbreakable, shares its roots with old names for diamond, and in crystal traditions it stands for endurance and commitment. Even so, diamond can chip if struck at the wrong angle, because hardness is not the same as toughness.

Why the gaps between the numbers are uneven

Because the scale is ordinal, the step from 1 to 2 is not the same size as the step from 9 to 10. The absolute hardness column above makes this clear. Talc and gypsum differ by only a little, while topaz (200) to corundum (400) doubles, and corundum to diamond (1500) nearly quadruples. In other words, diamond is about four times as hard as corundum even though they sit just one number apart.

This matters in two practical ways. First, a stone rated 9 is not “almost as hard” as diamond in any everyday sense. Second, half-steps such as 5.5 or 7.5 are useful labels for collectors but are not precise measurements. Scientists who need exact numbers use other methods, such as the Vickers, Knoop or Rockwell tests, which press a shaped point into the material and measure the dent. Mohs remains popular for a simple reason: you can do it in the field with a pocket kit.

There is also a technical detail behind the word “scratch”. For the scale, a scratch means a permanent groove visible to the naked eye. A softer mineral can sometimes leave microscopic damage on a harder one, but that does not count when assigning a number.

Where everyday objects and gemstones fall

You do not need a full kit to use the minerals on Mohs hardness scale tables, because many household objects sit at known points between them. These approximate values come from standard reference lists:

Gemstones you may already own also have rough places among the minerals on Mohs hardness scale charts. Opal sits around 5.5 to 6, jadeite around 6.5 to 7, garnet around 7 to 7.5, emerald 7.5 to 8, sapphire 9 and moissanite 9 to 9.5. Our gem hardness chart covers many more gemstones in one place, and the companion guide on gemstone hardness, toughness and care explains why a hard stone can still break.

Notice how opal sits barely above glass. That is useful context if you are choosing a birthstone ring; the birthstone colours by month guide lists alternatives for softer stones.

How to test hardness at home, step by step

A scratch test is one of the simplest ways to narrow down what a stone might be, and it pairs well with the other clues in our guide to telling whether a crystal is real. The goal is to find the softest material that scratches your stone and the hardest one it can scratch.

1. Choose a hidden spot. Use the base or back of the stone, never a polished face or a point you love. A scratch is permanent.
2. Gather your testers. Fingernail, copper coin, steel nail or knife, a glass tile or bottle base with smooth edges, and if you have them, a quartz point and pieces from a hardness kit.
3. Start soft and work upward. Press the tester firmly but gently and draw a short line, about the length of a grain of rice. Do not saw back and forth.
4. Wipe and look closely. Rub the line with a damp fingertip and inspect it with a hand lens. A softer tester often leaves a powdery trail that wipes away; a true scratch is a groove you can feel with a fingernail.
5. Test in reverse. Try scratching the tester with your stone. If each marks the other, they are close in hardness.
6. Bracket the result. Record the softest thing that scratched it and the hardest thing it scratched. Its hardness lies between the two.

A worked example

Imagine a translucent purple stone with flat, glassy faces. A fingernail leaves nothing, and neither does a copper coin. A steel nail leaves a clear groove that does not wipe away, so the stone is softer than about 4.5. The stone in turn scratches the copper coin. That places it somewhere around 3.5 to 4.5. Purple colour, flat breakage planes and a hardness near 4 all point toward fluorite rather than amethyst, which would have shrugged off the steel completely, since quartz sits at 7. One test rarely names a stone alone, but here it rules out the most common look-alike in under a minute.

Mistakes people make

• Testing the good side. Even a careful test leaves a mark. Always use a hidden edge.
• Mistaking powder for a scratch. If the line wipes off, the tester was softer and simply left its own dust behind.
• Testing a rock as if it were one mineral. Mixed stones such as granite give different answers in different places.
• Pressing too hard. Heavy pressure can crack or chip brittle stones, especially fluorite and topaz with their easy splitting directions.
• Testing dyed or coated pieces. A coating can scratch or flake on its own, giving a false reading about the stone beneath.
• Letting children run the test unsupervised. Steel points and broken glass need adult hands, and small crystal fragments should be kept away from little ones and pets.

Why hardness matters for crystal care

The most practical reason to learn the minerals on Mohs hardness scale lists is to protect your collection. Dust itself contains tiny quartz grains, so stones softer than 7 slowly lose their polish when wiped with a dry, gritty cloth. Harder stones in a shared pouch act like sandpaper on softer ones.

A few simple habits go a long way:

• Store by hardness. Keep stones of 5 and below in separate pouches or padded compartments. Corundum and topaz should never share a bag with calcite or fluorite.
• Choose jewelry with hardness in mind. Rings and bracelets take the most knocks, so harder stones such as quartz, topaz and sapphire suit them better. Softer stones shine in pendants and earrings.
• Clean gently. Use a soft, slightly damp cloth for most stones and a dry brush for the softest. Avoid abrasive pastes and salt scrubs.
• Pick cleansing rituals that suit the stone. Soft or water-sensitive minerals such as gypsum and calcite are better suited to smoke, sound or moonlight rituals than to long soaks. Our guide to cleansing crystals at home covers gentle options.
• Skip crystal elixirs with soft or unidentified stones. If you are unsure what a mineral is, do not place it in drinking water at all.

Hardness also explains why some stones are so rarely seen in jewelry at all, a point worth knowing before you browse a list of rare gemstones, where several beauties are simply too soft to wear.

Hardness in crystal traditions

Hardness has a quiet presence in crystal symbolism. In many traditions the hardest stones carry meanings of endurance and commitment: diamond for lasting bonds, sapphire for steadfast wisdom. Softer stones, such as selenite and calcite, are more often described as gentle, nurturing or light-filled, and people tend to keep them on altars and shelves rather than in pockets. These associations are beliefs, not properties you can measure, but they line up neatly with how the stones are actually handled.

Some collectors enjoy building a “hardness grid” during meditation, laying the ten reference minerals in order as a reminder that strength and softness both have their place. Others keep a small kit as a teaching set for children, a hands-on way to see that the world’s materials sit on a ladder. If you are starting such a set, browsing Spirit Magicka or a local rock show is a pleasant first step, and our crystal library has individual articles to read alongside each piece. You can also read how the journal approaches these beliefs on our editorial page.

Whichever way you use it, the scale rewards curiosity. Once you know that steel stops at around 4.5 and quartz holds at 7, every stone in your hand becomes a small puzzle you can solve, and every pouch in your collection becomes a little safer. Learn the ten minerals on Mohs hardness scale charts once, and they will serve you for every stone you collect afterward.