THE COLOURED STONES
An engagement ring is worn every day for decades. Before you fall for a stone, it helps to know how it will wear. Hardness, toughness and stability, and how the popular gemstones compare.
Gemmologists describe durability in three ways, and a stone needs all three to wear well every day:
Ordinary household dust contains particles of quartz, which sits at 7 on the Mohs scale. Any stone softer than quartz will gradually be scratched simply by being wiped and worn. Its facet edges soften and its polish dulls.
That is why, for a ring worn every day, we look for a stone at 7.5 or above, or we protect a softer stone with the design.
| Stone | Hardness (Mohs) | Everyday ring wear |
|---|---|---|
| Diamond | 10 | Excellent |
| Sapphire, ruby | 9 | Excellent, and very tough |
| Moissanite | 9.25 | Excellent |
| Spinel | 8 | Very good |
| Aquamarine, morganite | 7.5 to 8 | Very good |
| Emerald | 7.5 to 8 | Good, with a protective setting; inclusions reduce toughness |
| Tourmaline | 7 to 7.5 | Good, with care |
| Garnet | 6.5 to 7.5 | Fair to good, with care |
| Tanzanite | 6 to 7 | Fair; best protected, or worn as earrings or a pendant |
| Opal | 5.5 to 6.5 | Delicate; better for occasional wear |
| Pearl | 2.5 to 4.5 | Delicate; better for earrings and necklaces |
Some stones split easily along flat planes in the crystal, called cleavage. Even diamond has cleavage, which is why a hard knock on an exposed point can chip it. Tanzanite and topaz have distinct cleavage, which makes them more vulnerable to a sharp blow despite reasonable hardness.
Inclusions affect toughness too. Emerald is hard but often included, so it is more brittle than its hardness suggests.
Design can make a softer or more brittle stone wearable. A bezel encircles the edge. Raised shoulders or a halo take knocks before the stone does. A lower profile keeps the stone closer to the hand. Corners and points, such as the tip of a pear or marquise, can be protected with V-shaped claws.
Be honest about the life the ring will lead. For hands that are busy every day, diamond, sapphire and ruby are the safest choices. For a stone you love that is a little softer, choose a protective setting, take the ring off for the gym, gardening and cleaning, and plan for an occasional repolish.
Diamond is the hardest. Sapphire and ruby, at 9 on the Mohs scale, are exceptionally tough and are the most durable coloured stones.
We recommend 7.5 or above for daily wear. Softer stones can be worn with a protective setting and extra care.
Tanzanite is relatively soft and has distinct cleavage, so it needs a protective setting and gentle wear. It is often better suited to earrings or a pendant.
Hardness is resistance to scratching. Toughness is resistance to chipping and breaking. A stone can be hard but not tough.
Opal is soft and sensitive to knocks and dryness. It is better suited to occasional wear or a well-protected setting.
STILL HAVE QUESTIONS?
Bring the stone you have in mind, or the question, to a private appointment in central London or a video call. Consultations are complimentary.