Care desk / durability
Hardness is not toughness
The Mohs scale tells you how easily a stone scratches. It does not tell you how easily it breaks. Confusing the two is the most common reason people buy a "durable" stone and then chip it within a month.
What the Mohs scale actually measures
Mohs hardness ranks minerals from 1 (talc) to 10 (diamond) by whether one can scratch another. It is an ordinal scale, so the gaps are not equal: the jump from 9 to 10 is far larger than the jump from 1 to 2.
A hardness of 7, like quartz, resists everyday dust and most abrasion, which is why quartz jewelry wears well. But hardness says nothing about how a stone survives a knock against a doorframe or a drop onto tile.
Toughness: the part people forget
Toughness describes resistance to breaking, chipping, and fracturing. Some hard stones are surprisingly fragile because they have cleavage, a tendency to split along flat planes.
- Diamond is a 10 in hardness but has perfect cleavage, so a sharp blow in the wrong direction can still cleave it.
- Topaz (hardness 8) and kunzite (6.5-7) both have cleavage and can split under impact despite being reasonably hard.
- Jade is only 6-7 in hardness but is extremely tough because its interlocking fibrous structure resists fracture, which is why it survives carving and daily wear so well.
What this means for where you wear a stone
Rings and bracelets take constant impact against surfaces, so they need both hardness and toughness. Earrings and pendants are comparatively protected, so softer or more brittle stones are safer there.
A stone with hardness below 7 will gradually dull in a ring that brushes against counters, keys, and other jewelry. A stone with cleavage can crack even at high hardness. Match the stone to the setting, not just to its pretty color.
Inclusions: a hidden durability factor
Heavily included stones can be weaker along the inclusions. A fracture-filled stone can be damaged by heat, ultrasonic cleaning, or even a hard bump. This is why treatment and inclusion state belong in every care decision, not just hardness.
Related: how to clean crystal jewelry and natural versus treated stones.