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.

The "rule of 7" for everyday rings

Jewelers often advise the rule of 7 for rings you wear daily. The reason is simple: ordinary household dust is largely made of quartz, which sits at exactly 7 on the Mohs scale. A stone below 7 will gradually pick up micro-scratches as dust wipes across it, slowly clouding the polish. A stone at 7 or above resists that everyday dust, so it keeps its gloss far longer.

Protective settings for softer stones

You do not have to give up a softer stone if you love it. A prong setting leaves a stone's edges exposed to knocks and chips. A bezel setting, where a rim of metal wraps around the stone's edge, shields those vulnerable points and is the safer choice for stones below 7 or with noticeable cleavage.

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.