**Mohs Hardness Scale — Interactive Chart and Field Scratch Test**

> The full Mohs scale with the everyday tools that sit between each step, plus how to run a scratch test without ruining the specimen and why the scale is not proportional.

Source: https://orvik.app/tools/mohs-hardness-scale/ · updated: 2026-09-04

1. [Orvik](https://orvik.app/)

2. [Free tools](https://orvik.app/tools/)

3. Rocks & minerals

Rocks & minerals

# Mohs hardness scale, with a scratch test you can actually do

Pick a hardness and see what it scratches, what scratches it, and which household object sits at that level. The scale is **ordinal, not proportional** — the gap from 9 to 10 is bigger than the whole range from 1 to 9 — and that is the fact that makes it useful.

Steps **10** Field tools **8** Updated **2026-09-04** Cost **Free, no account**

Hardness Drag to a hardness step and read what it does and does not scratch.

Mohs

7

Quartz

- Field test **—**
- Absolute hardness **—**
- Scratches **—**
- Scratched by **—**
- Everyday equivalent **—**

## The scale, and the tools between the steps

*Mohs reference minerals with absolute (Knoop-scaled) hardness, showing how uneven the intervals are. Values follow standard mineralogical references.*

| Mohs | Reference mineral | Absolute | In the field |
| --- | --- | --- | --- |
| 1 | Talc | 1 | Crumbles under a fingernail; feels soapy |
| 2 | Gypsum | 2 | A fingernail (2.5) scratches it |
| 3 | Calcite | 9 | A copper coin (3.5) scratches it |
| 4 | Fluorite | 21 | A knife scratches it easily |
| 5 | Apatite | 48 | A knife scratches it with effort |
| 6 | Orthoclase feldspar | 72 | Scratches glass; a steel file (6.5) scratches it |
| 7 | Quartz | 100 | Scratches glass and steel easily |
| 8 | Topaz | 200 | Scratches quartz |
| 9 | Corundum — ruby and sapphire | 400 | Scratches topaz |
| 10 | Diamond | 1600 | Scratches everything |

### Common objects as reference points

- **Fingernail** — about 2.5 on the Mohs scale
- **Copper coin** — about 3.5 on the Mohs scale
- **Iron nail** — about 4.5 on the Mohs scale
- **Window glass** — about 5.5 on the Mohs scale
- **Pocket knife blade** — about 5.5 on the Mohs scale
- **Steel file** — about 6.5 on the Mohs scale
- **Quartz pebble** — about 7 on the Mohs scale
- **Masonry drill bit (tungsten carbide)** — about 8.5 on the Mohs scale

## What the scale actually measures

Friedrich Mohs published his scale in 1812 and it has survived unchanged for one reason: it needs nothing. Ten reference minerals, arranged so that each scratches the one below it, and a field geologist with a knife and a coin can place any specimen inside it in seconds.

What it measures is **scratch resistance** — resistance to having the surface bonds broken by a point drawn across it. It is not toughness, not strength, and not durability, and conflating those is where almost every misunderstanding of the scale begins.

It is also **ordinal, not proportional**. The intervals are not equal and were never intended to be. Measured on an absolute indentation scale, corundum at 9 is roughly four times as hard as topaz at 8, and diamond at 10 is roughly four times corundum again. The gap between 9 and 10 is larger than the gap between 1 and 9. That single fact explains why diamond is in a category of its own rather than one notch above ruby.

## Doing a scratch test without ruining the specimen

1. **Pick an inconspicuous spot on a fresh surface.** Weathered faces are softer than the interior of the same mineral, and a scratch across the display face of a good specimen is permanent.
2. **Press firmly and draw once**, a short stroke of a few millimetres. Repeated scrubbing produces a groove even in hard material and tells you nothing.
3. **Rub the mark with your thumb, then look.** This is the step everyone skips. A steel blade drawn across quartz leaves a grey line that looks exactly like a scratch and wipes straight off — that is metal deposited on the mineral, and it means the mineral is harder than the steel, the opposite of what it looks like.
4. **Confirm with a hand lens.** A real scratch is a continuous groove that catches light along its length.
5. **Work upward.** Start with a fingernail and move up through coin, knife, glass and file until something bites. That brackets the hardness between two values, which is all a scratch test can ever give you.

Two properties will mislead you. **Cleavage** can make a mineral flake away under a point, which looks like a soft scratch and is not — a nail drawn across mica or gypsum along the cleavage plane peels a sheet off. And **hardness can be directional**: kyanite is about 4.5 measured along the length of its blades and about 7 measured across them, which is diagnostic for the species and which will look like a contradictory result if you do not know to expect it.

## Hard is not the same as tough

Diamond is the hardest natural substance and it will shatter if you hit it with a hammer on the right plane. Jade is only 6 to 7 and it is so tough that it was used for axe heads and adzes for thousands of years. These are different properties and the confusion has practical consequences.

*Four properties routinely bundled together as "hardness", and what each actually means.*

| Property | Meaning | High example | Low example |
| --- | --- | --- | --- |
| Hardness | Resistance to being scratched | Diamond, corundum | Talc, gypsum |
| Toughness | Resistance to breaking or chipping | Jade, nephrite | Diamond, topaz, tanzanite |
| Stability | Resistance to heat, light and chemicals | Quartz, corundum | Opal, pearl, amber |
| Cleavage | Tendency to split along planes | Mica, fluorite, topaz | Quartz, garnet — none |

Two consequences worth carrying around. Topaz is an 8 and has perfect basal cleavage, so a topaz ring survives everyday abrasion beautifully and can split from one sharp knock on a doorframe. Opal is only 5.5 to 6.5 and, more importantly, holds water in its structure, so it crazes with dry heat regardless of how carefully it is protected from scratching.

## The jewellery rule that follows from all this

The single most useful number in the whole scale is **7**, because ordinary household dust contains quartz. Anything softer than 7 is being sanded by the air it sits in, slowly, forever.

This is why the practical guidance for a stone worn every day — an engagement ring, in particular — is to stay at or above 7, and preferably above 8. Diamond at 10, sapphire and ruby at 9, spinel at 8, and topaz at 8 with the cleavage caveat all qualify. Emerald is nominally 7.5 to 8 but is usually heavily included and frequently oil-treated, which makes it far less durable than the number suggests. Tanzanite at 6 to 7 and opal at 5.5 to 6.5 are genuinely unsuited to daily wear on a hand and are far better in earrings or a pendant, where nothing hits them.

The same logic governs stone countertops. Granite is dominated by quartz and feldspar at 6 to 7 and shrugs off knives; marble is calcite at 3 and both scratches and etches on contact with lemon juice or vinegar, which is a chemical reaction rather than an abrasion and cannot be prevented by sealing. Quartzite is a different rock again and is harder than granite. The trade names in a showroom are unreliable, and a scratch test on a sample offcut settles it in ten seconds.

## Testing a suspected gemstone or a diamond

Hardness is a useful screening tool for gem identification and a poor final answer. Two rules keep it honest.

**Never scratch a faceted stone.** Test on the girdle — the thin unpolished band around the widest part — or better, do not scratch it at all. A visible scratch on a table facet destroys value.

**Hardness cannot distinguish a diamond from its two best simulants.** Moissanite is 9.25 and cubic zirconia is 8 to 8.5; both scratch glass effortlessly, so the classic "it scratches glass so it must be a diamond" test proves nothing at all. The properties that do separate them are thermal conductivity, which is what a jeweller's diamond tester measures, and double refraction, which moissanite shows and diamond does not — look through the table at the opposite facet edges under magnification and moissanite doubles them.

The reverse test is more useful than the forward one: **anything a steel knife scratches easily is not a diamond, a sapphire, a ruby or a topaz.** That eliminates a great deal quickly. For anything that survives it and matters financially, the answer is a gemmological laboratory rather than a kitchen table.

## Questions people ask about this

How do I test hardness at home?

Work upward through the tools you already have: fingernail at about 2.5, a copper coin at 3.5, a knife blade or window glass at 5.5, a steel file at 6.5, a quartz pebble at 7. Draw one firm short stroke on a fresh inconspicuous surface, then rub the mark with your thumb before judging it — a steel blade leaves a grey metal smear on hard minerals that looks exactly like a scratch and wipes off.

Is a diamond twice as hard as ruby?

No — far more than twice. The Mohs scale is ordinal, not proportional, and the intervals are deliberately unequal. On an absolute indentation scale corundum at 9 is roughly four times as hard as topaz at 8, and diamond at 10 is roughly four times corundum again. The single step from 9 to 10 is a larger jump than the whole range from 1 to 9.

What hardness does a ring stone need for daily wear?

Seven or above, and preferably eight, because ordinary household dust contains quartz at 7 and will slowly abrade anything softer. Diamond, sapphire, ruby and spinel are all comfortably in range. Opal, tanzanite, pearl and turquoise are not, and belong in earrings or a pendant where nothing strikes them.

Why is jade tough if it is only 6 or 7?

Because hardness and toughness are different properties. Hardness is resistance to scratching; toughness is resistance to breaking. Jade is made of densely interlocked fibrous crystals, which makes it extraordinarily resistant to fracture — it was used for axe heads for millennia. Diamond, by contrast, is the hardest natural material and will cleave from a well-placed blow.

Does scratching glass prove it is a diamond?

No. Glass is only about 5.5, so quartz, topaz, garnet, moissanite and cubic zirconia all scratch it easily. The test only rules things out — anything a knife scratches is not a diamond. Distinguishing diamond from moissanite needs thermal conductivity or a check for double refraction, and from cubic zirconia needs density or thermal testing.

Can hardness vary within one mineral?

Yes, and kyanite is the classic demonstration: about 4.5 measured along the length of its blades and about 7 measured across them, because the bonding differs by direction. Diamond is also anisotropic, which is exactly what makes it possible to cut a diamond with another diamond. Weathering also softens the outside of most specimens, which is why the test belongs on a fresh surface.

Why does my marble countertop scratch and stain so easily?

Marble is recrystallised calcite, hardness 3, so almost anything harder than a fingernail marks it. Worse, calcite reacts with acid, so lemon juice, vinegar and wine etch dull spots into the polish through a chemical reaction that sealing does not prevent. Granite is 6 to 7 and quartzite is harder still. Showroom names are unreliable — take an offcut and try a knife on it.

## Got the hardness but not the mineral?

Hardness brackets a specimen; it rarely names it. Photograph the rock and Orvik proposes the species, then check the call against the streak, lustre and cleavage in the mineral key.

- [Get Orvik free](https://orvik.app/app/)

## Keep reading on Orvik

- [What is the hardest rock?](https://orvik.app/rocks/what-is-the-hardest-rock/)

- [How to identify rocks](https://orvik.app/rocks/identify-rocks/)

- [Quartz identification](https://orvik.app/rocks/quartz-identification/)

- [Gemstone identification](https://orvik.app/rocks/gemstone-identification/)

- [Crystal identifier](https://orvik.app/rocks/crystal-identifier/)

- [How to identify igneous rocks](https://orvik.app/rocks/how-to-identify-igneous-rocks/)

- [What is this rock?](https://orvik.app/rocks/what-is-this-rock/)

- [What is a geode?](https://orvik.app/rocks/what-is-a-geode/)

## Other free Orvik tools

- [What kind of rock is this?](https://orvik.app/tools/rock-identifier/)
- [Which mineral is this?](https://orvik.app/tools/mineral-identifier/)
- [What gemstone is this?](https://orvik.app/tools/gemstone-identifier/)
- [What fossil is this?](https://orvik.app/tools/fossil-identifier/)
- [What animal made this track?](https://orvik.app/tools/animal-track-identifier/)
- [Whose droppings are these?](https://orvik.app/tools/animal-scat-identifier/)
- [What snake did I just see?](https://orvik.app/tools/snake-identifier/)
- [Whose egg is this?](https://orvik.app/tools/bird-egg-identifier/)

## Where the data comes from

- [US Geological Survey — Mohs scale of mineral hardness](https://www.usgs.gov/programs/mineral-resources-program)
- [Mindat — hardness and physical properties](https://www.mindat.org/)
- [GIA — gemstone durability, hardness, toughness and stability](https://www.gia.edu/gem-encyclopedia)
- [Mineralogical Society of America](https://msaweb.org/)

---

HTML version: https://orvik.app/tools/mohs-hardness-scale/
Structured data for this site: https://orvik.app/api/v1/openapi.json · https://orvik.app/llms.txt
Free to quote and reuse with a link back to the source URL above (CC BY 4.0).