Mohs Hardness Scale

Data

Source: Wikipedia — Mohs scale of mineral hardness. Absolute hardness values are approximate Vickers hardness ratios relative to talc.

Note: What You Should Know About Mineral Hardness

The Mohs hardness scale is the classic, everyday way we rank how well minerals resist being scratched. It was invented by the German geologist Friedrich Mohs in 1812, and even though it’s over two centuries old, it’s still the go-to scale in classrooms, field geology kits, and jewellers’ benches. The idea is wonderfully simple: pick ten known minerals, arrange them from softest to hardest, and use any one of them to scratch any material you meet. Whatever scratches it tells you how hard it is.

How the Scale Works

• Minerals are ranked 1 to 10: 1 is the softest, 10 is the hardest.
• Talc (1) is so soft you can scratch it with a fingernail — it’s literally the powder in talcum powder.
• Gypsum (2) can be scratched by a fingernail too, which is why drywall crumbles so easily.
• Copper pennies (~3), a steel pocketknife (~5.5), and a hardened steel file (~6.5) are handy reference tools for field tests.
• Quartz (7) is the key boundary: it scratches ordinary glass and steel, so anything that resists quartz is genuinely tough.
• Corundum (9) is the natural gem mineral here — ruby and sapphire are both corundum, exactly the same mineral in different colours.
• Diamond (10) tops the chart as the hardest known natural mineral.

The Scale Is Ordinal, Not Linear

Here’s a subtle but important point: Mohs is a ranked, relative scale, not a linear one. A jump from 9 to 10 is a far bigger leap in real hardness than a jump from 1 to 2. That’s why the table shows “absolute hardness” numbers — those approximate Vickers ratios make the real gaps visible:

• Diamond (rated 10, absolute ~1500) is only one step above corundum on the Mohs scale, yet it’s more than three times harder in absolute terms.
• Corundum (9, ~400) vs. topaz (8, ~200) is another near-doubling of absolute hardness.
• Compare that to the bottom: talc (1, ~1) to gypsum (2, ~3) — tiny absolute differences.
• So Mohs tells you the order, while absolute hardness figures tell you the size of the gaps.

Hardness ≠ Everything Else

• Hardest is not the same as strongest. Diamond is extremely hard (resists scratching) but it is also brittle — a single sharp blow can cleave or shatter it, which is exactly how jewellers and cutters work with it.
• Hardness is not chemical inertness. Diamond is just pure carbon, so at high temperature in air it can burn back to carbon dioxide. “Hardest” and “most chemically stable” are completely different properties.
• Don’t confuse hardness with toughness, durability, or density — each mineral property is measured its own way.

Fun Facts

• Mohs actually built his scale by rubbing minerals against each other in a workshop — no machines, just careful scratch tests.
• Diamond is not only the hardest natural mineral, but in the Mohs ranking there is a hardness cliff between corundum (9) and diamond (10).
• A fingernail hardness is about 2.5, a copper coin about 3.5, and window glass around 5.5 — handy everyday benchmarks.
• Even though diamond tops mineral hardness, synthetic materials like some carbides used in industry can scratch tougher in engineered applications — a fun debate for mineral purists.
• Because it is all about scratching, the scale works best on smooth, fresh surfaces — weathered or coated samples can fool a casual test.
• Geologists still keep a set of right around 10-fingernail-through-diamond reference minerals in their field kits today.

Bottom line: the Mohs scale is a brilliant, portable ordering tool that you can use anywhere — just remember it compares order, not absolute strength. When you need the full picture, pair it with the absolute hardness figures in the table above.