Jewellery Guide
Know Your Gemstone
Colour, treatments, and hardness — a practical guide
Gemstones bring colour, symbolism, and character to jewellery. Understanding colour quality, common treatments, and hardness helps you choose a stone that suits both your taste and how you plan to wear it.
Gemstones bring colour and character to jewellery in a way metal alone cannot. Each stone has its own personality — in colour, hardness, and how it should be worn and cared for. This guide introduces the most popular gemstones and what to look for when choosing one.
Precious vs. Semi-Precious Gemstones
Traditionally, "precious" gemstones referred to ruby, emerald, sapphire, and diamond, while every other gemstone was labelled "semi-precious." In practice, this old classification says little about actual value — a fine-quality tanzanite or spinel can be rarer and pricier than a lower-grade sapphire. Today, a gemstone's worth is judged on its own colour, clarity, rarity, and craftsmanship rather than this historical label.
Popular Gemstones at a Glance
Ruby
A red variety of the mineral corundum, ruby is prized for a vivid, slightly purplish-red colour often described as "pigeon's blood" at its finest. Most rubies contain natural inclusions called "silk," which can soften light and add character without necessarily reducing beauty.
Emerald
A green variety of beryl, emerald's value depends heavily on colour saturation and evenness. Emeralds almost always contain visible inclusions (sometimes called "jardin," French for garden) — this is considered normal and expected, not a defect, and most emeralds are treated with oil to improve clarity's appearance.
Sapphire
Also a variety of corundum (the same mineral family as ruby), sapphire is best known in blue but occurs in nearly every colour except red. Cornflower and royal blue tones are especially prized. Sapphire is highly durable, making it a popular alternative centre stone for engagement rings.
Pearl
Unlike mined gemstones, pearls are organic, formed inside molluscs. Cultured pearls (grown with human intervention) dominate the market today; quality is judged on lustre, surface smoothness, shape, and colour. Pearls are softer than most gemstones and need gentler care.
Amethyst, Topaz, Aquamarine, and Opal
- Amethyst — a purple variety of quartz, valued for rich, even colour saturation.
- Topaz — occurs naturally in blue, yellow, and pink tones; much blue topaz on the market is treated to enhance or create its colour.
- Aquamarine — a pale blue-green variety of beryl (the same family as emerald), valued for clarity and a cool, calming tone.
- Opal — known for "play-of-colour," a shifting rainbow effect caused by its internal structure; it's softer and more porous than most gemstones, requiring extra care.
Tanzanite
A blue-violet gemstone found in only one location on earth, near Mount Kilimanjaro in Tanzania. Its relative rarity and rich colour have made it a popular alternative to sapphire, though it's softer and needs more careful handling.
Birthstones
| Month | Birthstone |
|---|---|
| January | Garnet |
| February | Amethyst |
| March | Aquamarine |
| April | Diamond |
| May | Emerald |
| June | Pearl |
| July | Ruby |
| August | Peridot |
| September | Sapphire |
| October | Opal |
| November | Topaz |
| December | Tanzanite |
Treatments: What's Normal in the Trade
Most coloured gemstones on the market are treated in some way to improve their appearance or stability — this is an accepted, widespread practice, not a red flag, provided it's disclosed. Common treatments include heat treatment (used on ruby and sapphire to improve colour and clarity), oiling (used on emerald to fill surface-reaching fractures), and dyeing (used on more porous stones). Ask your jeweller whether a stone is treated and how — this affects both its care requirements and, sometimes, its price.
Hardness and the Mohs Scale
The Mohs scale ranks a mineral's resistance to scratching, from 1 (talc) to 10 (diamond). It's a useful guide for choosing which gemstones suit daily-wear pieces like rings versus more protected pieces like pendants and earrings.
| Gemstone | Mohs Hardness |
|---|---|
| Diamond | 10 |
| Sapphire / Ruby (Corundum) | 9 |
| Topaz | 8 |
| Aquamarine / Emerald (Beryl) | 7.5–8 |
| Amethyst (Quartz) | 7 |
| Tanzanite | 6–7 |
| Opal | 5.5–6.5 |
| Pearl | 2.5–4.5 |
Gemstones with a Mohs hardness below 7 — including opal, pearl, and tanzanite — are better suited to earrings, pendants, and occasional-wear rings than pieces exposed to daily friction.
Caring for Gemstone Jewellery
- Clean with a soft, damp cloth; avoid ultrasonic and steam cleaners for softer or treated stones like emerald, opal, and pearl.
- Store gemstone pieces separately, ideally in soft pouches, to prevent scratching from harder stones or metal edges.
- Remove gemstone jewellery before swimming, exercising, or applying perfume, lotion, or hairspray — chemicals can dull colour or damage porous stones.
- Have prong settings checked periodically, especially for rings worn daily.
Buying Guide
Prioritise colour first for coloured gemstones — it's usually the biggest driver of both beauty and value. Ask about treatments and get them disclosed in writing for higher-value stones. Match the gemstone's hardness to how the piece will be worn, and choose a setting (like a bezel or halo) that protects softer stones from daily knocks.
Key Takeaways
- The old "precious vs. semi-precious" label says little about real value — colour, clarity, and rarity matter more.
- Most coloured gemstones are treated (heated, oiled, or dyed) to improve appearance — this is standard practice when disclosed.
- The Mohs hardness scale helps match a gemstone to how it will be worn: below 7 suits earrings and pendants better than daily-wear rings.
- Inclusions in emerald ("jardin") and silk in ruby are natural and expected, not necessarily defects.
- Clean gemstone jewellery gently with a damp cloth — avoid ultrasonic cleaners for softer or treated stones.
Frequently Asked Questions
Is a treated gemstone less valuable than an untreated one?
Not necessarily lower quality, but untreated stones of comparable colour and clarity are rarer and typically command a higher price. Most gemstones on the market are treated in some standard, industry-accepted way, and this should simply be disclosed to you.
Can I wear an emerald or opal ring every day?
It's possible but requires care — both are softer and more prone to chipping or scratching than diamond or sapphire. A protective setting like a bezel, and avoiding rough activity while wearing the ring, helps extend its life.
What does "pigeon's blood" mean for rubies?
It's a trade term describing the finest, most saturated red colour in ruby — a vivid red with a slight purplish tone and no visible brown or grey undertone.
How do I clean pearl jewellery?
Wipe pearls with a soft, slightly damp cloth after wearing to remove oils and perspiration. Avoid ultrasonic cleaners, harsh chemicals, and perfume contact, and store pearls flat or in a soft pouch, separate from harder gemstones.
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