Customers ask me all the time if a stone is going to scratch. Sapphire, topaz, turquoise, opal, it comes up with almost every gemstone I set. The Mohs hardness scale is the closest thing we have to a straight answer, and it's worth understanding on its own terms rather than picking up secondhand from a product description.
What the Scale Actually Measures
Hannes Grobe - CC BY 3.0
The test behind Mohs hardness is simple. If one mineral can scratch another, it's the harder of the two. Run that comparison against a set of ten reference minerals and you get a ranking from 1, talc, up to 10, diamond.
Friedrich Mohs put this scale together in the early 1800s, and it's still the standard reference for gem and mineral hardness today. It's a ranking, not a measurement of anything physical like force or pressure. That distinction matters more than it sounds like it should, and I'll come back to it.
The 1 to 10 Reference Scale
Here's the full scale, with what each point tends to mean for jewelry.
| Mohs | Reference mineral | Jewelry translation |
|---|---|---|
| 1 | Talc | Softest reference point. Not a jewelry material. |
| 2 | Gypsum | Still gives way to a fingernail in most cases. |
| 3 | Calcite | Too soft for hard-wearing jewelry. |
| 4 | Fluorite | Attractive, but not durable enough for daily wear. |
| 5 | Apatite | Middling on the scale, still easy to scratch in normal use. |
| 6 | Orthoclase feldspar | Harder than apatite, but still below the quartz threshold. |
| 7 | Quartz | The practical durability line. Includes citrine and amethyst. |
| 8 | Topaz | Very scratch-resistant, but watch the note on toughness below. |
| 9 | Corundum | Sapphire and ruby. Excellent scratch resistance. |
| 10 | Diamond | The hardest known mineral. |
One thing this table can't show you: the scale isn't evenly spaced. The jump from 9 to 10 represents a much bigger real-world difference than the jump from 2 to 3. Diamond isn't "a little harder" than sapphire, it's dramatically harder. Treat Mohs as a ranking, not a ruler.
Where the Stones I Work With Land
Here's how the gemstones I use most often stack up.
| Stone | Mohs hardness |
|---|---|
| Diamond | 10 |
| Sapphire / Ruby | 9 |
| Topaz | 8 |
| Quartz family (citrine, amethyst) | 7 |
| Agatized (fossilized) coral | 6.5 to 7 |
| Turquoise | 5 to 6 |
| Opal | 5 to 6.5 |
| Pearl | 2.5 |
That agatized coral entry is worth a note on where the number comes from. Coral itself starts out soft and organic. What we work with isn't raw coral, it's fossilized coral that's spent millions of years having its original structure replaced by silica in the form of agate. That transformation is what pushes the hardness up into the 6.5 to 7 range. It's a different material by the time it reaches the bench.
Hard Doesn't Mean Unbreakable
This is the part of the Mohs scale that gets skipped, and it's the part that actually matters for a ring you wear every day.
Hardness only measures scratch resistance. It says nothing about toughness, which is a stone's resistance to chipping and breaking, or about stability, which is how well a stone holds up to heat, chemicals, and light. A stone can score high on one and low on another.
Topaz is the clearest example already in our own catalog. It's an 8 on the Mohs scale, genuinely scratch-resistant, but it has a cleavage plane that makes it prone to chipping from a sharp knock. Diamond, at the very top of the scale, isn't immune either. It can still chip or fracture if it's struck hard at the wrong angle. A high Mohs number is a real advantage. It's not a guarantee that a stone can take a hit.
Sapphire, one step down from diamond at 9, doesn't have that same cleavage complication, which is part of why sapphire is such a dependable stone for a ring you wear daily.
What This Means for a Ring You Actually Wear
Black Fossilized Brain Coral Black Diamond Ebony Wood Silver Ring
Roughly, here's how I think about it.
Stones at 7 and above, sapphire, topaz, the quartz family, hold up well to daily wear with ordinary care. That's the range where I don't think twice about setting a stone in a ring meant to be worn every day.
Sleeping Beauty turquoise sits lower, in the 5 to 6 range. I use it often, but I lean toward earrings, pendants, or a protected setting over an everyday ring, since those see less knocking around.
Opal runs similar territory, 5 to 6.5, and gets the same consideration.
Pearl, at 2.5, needs the gentlest handling of anything I work with and should be stored on its own.
Quartz's spot at 7 isn't arbitrary either. It's simply the most common mineral you're likely to brush up against day to day. You're a lot more likely to catch a ring on a stray bit of quartz than a stray bit of sapphire, so 7 is roughly where a stone stops having to worry about ordinary contact with the world scratching it.
Storage Matters Just as Much
None of this hardness talk means anything if two stones end up sharing the same pouch. Drop a 9 rated sapphire piece in with a 6 rated turquoise piece, let them knock around in a bag or a drawer for a few months, and the turquoise will show it. It doesn't take a drop or a hard knock, just ordinary contact over time.
Keep harder and softer stones separated, in their own compartments or soft pouches, and hardness stops being something you have to think about day to day. The same separation principle is behind how I recommend storing wooden jewelry, and it holds whether the pieces in question are wood, gemstone, or both.
Not the Same Scale as Wood
The Crown Ring (Peroba Rosa Wood & 14k Rose Gold)
If you're weighing a wooden piece instead of a gemstone one, Mohs isn't the number you want. Wood hardness is measured on the Janka scale, which tests how much force it takes to press a steel ball into the wood. It's a different test measuring a different kind of durability, and the numbers don't translate between the two scales. If wood is what you're comparing, the Janka hardness scale is the post to read instead.
A Ranking, Not a Promise
Mohs hardness tells you what can scratch what. That's genuinely useful when you're choosing a stone or figuring out how to store it. It's not a promise that a high number means nothing can go wrong. Pair the hardness with how you actually wear and care for the piece, and any of these stones, hard or soft, can hold up for a long time.
If you're deciding between stones for a custom piece, reach out about a custom order and we can talk through what fits how you'll actually wear it.
Mohs figures in this post are referenced from the Mineralogical Society of America, Geology.com, and the GIA.
