Engagement Rings in the UK: Choosing a Coloured Gemstone

Diamonds still dominate the high street, but plenty of couples are now asking a different question: what if the centre stone were green, blue or pink? The honest answer is that a coloured gemstone can make a wonderful ring, as long as its hardness, clarity and setting suit the life you actually lead. Aquamarine engagement rings, for instance, are calm and clean, while an emerald and tourmaline engagement ring brings richer personality and a few quirks.

This guide explains how to judge each stone, compare them fairly and buy with confidence.

What Makes a Coloured Gemstone Right for an Engagement Ring?

A good coloured gemstone for an engagement ring combines enough hardness to survive daily wear, a strong and even colour, and clarity that suits the type of stone. As a general guideline, aim for a Mohs hardness of 7.5 or higher, and use a sensible setting to protect softer or more included stones.

Hardness is only half the story.

Mohs hardness measures scratch resistance and nothing else. On the Mohs scale, the standard reference taught to UK gemmologists through Gem-A (the Gemmological Association of Great Britain), diamond scores 10 and sapphire 9, while emerald and aquamarine both sit at 7.5 to 8 and tourmaline at 7 to 7.5. Household dust contains quartz, which scores 7, so anything below that will slowly dull.

Here’s a mildly contrarian view: hardness is overrated as a buying rule. Toughness, meaning resistance to chipping, matters just as much, and even a diamond can cleave if it takes a sharp knock at the wrong angle. A 7.5 stone in a well-made protective setting will often outlast a harder one worn carelessly.

Colour, clarity and the eye-clean test

Colour is what you pay for. Unlike diamonds, where colourless is the goal, a coloured stone is valued first on the strength, evenness and purity of its hue. View it in daylight and under warm indoor bulbs, because some stones shift noticeably between the two.

Clarity expectations vary by gem. Gemmologists expect aquamarine engagement rings to be clean to the naked eye, whereas emerald almost always shows inclusions. Judging an emerald by diamond standards is a classic buyer’s error.

Cut and carat weight

Coloured stones are cut to show off colour rather than to fixed proportions, so a slightly deep stone isn’t automatically a terrible one. Carat weight needs care too. Therefore, always ask for millimetre dimensions, not just carats.

How Do Emerald, Aquamarine and Tourmaline Compare?

Emerald offers the deepest green and the most character but demands the most care. Aquamarine is the cleanest and calmest, a soft sea-blue that’s easy to wear. Tourmaline gives the widest colour choice, from mint green to vivid pink, at a gentler price, though it’s marginally softer than the other two.

Emerald

Emerald is the green variety of beryl, coloured by trace chromium and sometimes vanadium. Its inclusions are known in the trade as the jardin, French for garden, and they’re part of its identity. Many stones also have surface-reaching fractures filled with oil or resin, which is standard practice but should always be disclosed.

That’s why the best emerald engagement rings UK jewellers make lean on bezel, halo or low claw settings. Prefer a stone that’s lively and well coloured over one that’s flawless, because a truly flawless emerald would be extraordinarily expensive. And if you work with your hands all day, it may simply not be the right fit.

Aquamarine

Aquamarine is also beryl, but its pale blue comes from iron, and it forms in large, clean crystals. That’s why you’ll rarely see heavy inclusions. Heat treatment to remove a greenish tint is common, stable and widely accepted in the trade.

The weakness? Very pale stones can look washed out against bright white metal. Choose a stone with some visible saturation, and view it next to the metal you’re considering before you commit.