Hardness of gemstones ranked
If you ever researched a gemstone you likely came across a reference to the Mohs Scale of Hardness. But what does this scale actually tell us?
The scale ranks different materials from 1 to 10, based on their resistance to scratching and abrasion. This means that each mineral can only be scratched by another material that is harder, or above it on this scale. With diamond being the highest on the scale, it can only be scratched by another diamond. But a tanzanite could be scratched by a sapphire and gold can be scratched by malachite.
One thing to keep in mind: the Mohs scale is not linear. The difference between 10 and 9 is significantly larger than that between 9 and 8 (see picture below), simply because diamond is so much harder than any other gem. So, when you hear sapphire is a 9, that does not mean it's invincible and you still want to practice caution when wearing sapphire jewelry. Remember that even diamond at 10 can chip and break when exposed to enough impact, so make sure you take good care of all your jewelry!
Hardness does not equal durability
So why does diamond still chip if it's a 10? Simply because the scale only ranks scratch resistance of gemstones but not their overall durability. Durability is a gemstone’s ability to withstand wear and elements such as heat, light, or humidity. When evaluating overall durability of gems, hardness is only one of the many factors. You also need to consider toughness, and stability to get a full picture.
Gemstone toughness
Toughness is defined as the stones resistance to breaking and chipping. This is defined by the structure of each mineral and is measured by the ability of a gemstone to withstand mechanical shock. On this scale, nephrite is the winner and jadeite is the runner up. Those two are the toughest stones, although they are much easier to scratch (both are around a 6.5 on the Mohs scale). Diamond is not the toughest stone and it can break, especially in certain directions. This is why diamonds with very thin girdles and those with pointy edges, like pear or marquise cuts, are more likely to chip and break.
Overall, remember that gemstones can be very hard but not tough and vice versa. While the Mohs scale is a great tool to understand which stones will scratch faster with daily wear, it doesn't tell a full story and by itself is only semi-helpful. But because scratches can make our jewelry look dull, the Mohs scale is helpful in making sure we avoid obvious mistakes, such as:
- Keeping your jewelry in a pouch where it constantly rubs on other gems and metals
- Stacking rings too frequently or wearing them too close to each other
- Leaving jewelry outside to collect dust, which scratches many softer stones
- Assuming your diamond is unbreakable
- Setting stones intended for daily wear too high, which exposes them to more impact
- Wearing jewelry at the gym or when doing heavy lifting
As a rule of thumb, jewelry is more fragile than you think. We recommend taking all your jewels in at least once a year to get checked for chips and loose prongs.
